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<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"/><meta name="viewport" content="width=device-width, initial-scale=0.8"/><title>6.7 Object and Class Contracts</title><link rel="stylesheet" type="text/css" href="../scribble.css" title="default"/><link rel="stylesheet" type="text/css" href="extras.css" title="default"/><link rel="stylesheet" type="text/css" href="../racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-style.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../manual-racket.css" title="default"/><link rel="stylesheet" type="text/css" href="../doc-site.css" title="default"/><script type="text/javascript" src="../scribble-common.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../manual-racket.js"></script><script type="text/javascript" src="../doc-site.js"></script><script type="text/javascript" src="../local-redirect/local-redirect.js"></script><script type="text/javascript" src="../local-redirect/local-user-redirect.js"></script><!--[if IE 6]><style type="text/css">.SIEHidden { overflow: hidden; }</style><![endif]--></head><body id="doc-racket-lang-org"><div class="tocset"><div class="tocview"><div class="tocviewlist tocviewlisttopspace"><div class="tocviewtitle"><table cellspacing="0" cellpadding="0"><tr><td style="width: 1em;"><a href="javascript:void(0);" title="Expand/Collapse" class="tocviewtoggle" onclick="TocviewToggle(this,"tocview_0");">►</a></td><td></td><td><a href="index.html" class="tocviewlink" data-pltdoc="x">The Racket Reference</a></td></tr></table></div><div class="tocviewsublisttop" style="display: none;" id="tocview_0"><table cellspacing="0" cellpadding="0"><tr><td align="right">1 </td><td><a href="model.html" class="tocviewlink" data-pltdoc="x">Language Model</a></td></tr><tr><td align="right">2 </td><td><a href="notation.html" class="tocviewlink" data-pltdoc="x">Notation for Documentation</a></td></tr><tr><td align="right">3 </td><td><a href="syntax.html" class="tocviewlink" data-pltdoc="x">Syntactic Forms</a></td></tr><tr><td align="right">4 </td><td><a href="data.html" class="tocviewlink" data-pltdoc="x">Datatypes</a></td></tr><tr><td align="right">5 </td><td><a href="structures.html" class="tocviewlink" data-pltdoc="x">Structures</a></td></tr><tr><td align="right">6 </td><td><a href="mzlib_class.html" class="tocviewselflink" data-pltdoc="x">Classes and Objects</a></td></tr><tr><td align="right">7 </td><td><a href="mzlib_unit.html" class="tocviewlink" data-pltdoc="x">Units</a></td></tr><tr><td align="right">8 </td><td><a href="contracts.html" class="tocviewlink" data-pltdoc="x">Contracts</a></td></tr><tr><td align="right">9 </td><td><a href="match.html" class="tocviewlink" data-pltdoc="x">Pattern Matching</a></td></tr><tr><td align="right">10 </td><td><a href="control.html" class="tocviewlink" data-pltdoc="x">Control Flow</a></td></tr><tr><td align="right">11 </td><td><a href="concurrency.html" class="tocviewlink" data-pltdoc="x">Concurrency and Parallelism</a></td></tr><tr><td align="right">12 </td><td><a href="Macros.html" class="tocviewlink" data-pltdoc="x">Macros</a></td></tr><tr><td align="right">13 </td><td><a href="input-and-output.html" class="tocviewlink" data-pltdoc="x">Input and Output</a></td></tr><tr><td align="right">14 </td><td><a href="security.html" class="tocviewlink" data-pltdoc="x">Reflection and Security</a></td></tr><tr><td align="right">15 </td><td><a href="os.html" class="tocviewlink" data-pltdoc="x">Operating System</a></td></tr><tr><td align="right">16 </td><td><a href="memory.html" class="tocviewlink" data-pltdoc="x">Memory Management</a></td></tr><tr><td align="right">17 </td><td><a href="unsafe.html" class="tocviewlink" data-pltdoc="x">Unsafe Operations</a></td></tr><tr><td align="right">18 </td><td><a href="running.html
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form: external and internal contracts. External contracts govern behavior
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when an object is instantiated from a class or when methods or fields are
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accessed via an object of that class. Internal contracts govern behavior
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when method or fields are accessed within the class hierarchy. This
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separation allows for stronger contracts for class clients and weaker
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contracts for subclasses.</p><p>Method contracts must contain an additional initial argument which corresponds
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to the implicit <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._this%29%29" class="RktStxLink" data-pltdoc="x">this</a></span> parameter of the method. This allows for
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contracts which discuss the state of the object when the method is called
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(or, for dependent contracts, in other parts of the contract). Alternative
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contract forms, such as <span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._-~3em%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>m</a></span>, are provided as a shorthand
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for writing method contracts.</p><p>Methods and fields listed in an <span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._absent%29%29" class="RktStxLink" data-pltdoc="x">absent</a></span> clause must <span class="emph">not</span> be present in the class.</p><p>A class contract can be specified to be <span class="emph">opaque</span> with the <span class="RktPn">#:opaque</span>
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keyword. An opaque class contract will only accept a class that defines
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exactly the external methods and fields specified by the contract. A contract error
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is raised if the contracted class contains any methods or fields that are
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not specified. Methods or fields with local member names (i.e., defined with
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<span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._define-local-member-name%29%29" class="RktStxLink" data-pltdoc="x">define-local-member-name</a></span>) are ignored for this check if
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<span class="RktPn">#:ignore-local-member-names</span> is provided.</p><p>The external contracts are as follows:</p><ul><li><p>An external method contract without a tag describes the behavior
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of the implementation of <span class="RktVar">method-id</span> on method sends to an
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object of the contracted class. This contract will continue to be
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checked in subclasses until the contracted class’s implementation is
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no longer the entry point for dynamic dispatch.</p><p>If only the field name is present, this is equivalent to insisting only
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that the method is present in the class.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">woody%</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._class%29%29" class="RktStxLink" data-pltdoc="x">class</a></span><span class="hspace"> </span><span class="RktSym"><a href="createclass.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._object~25%29%29" class="RktValLink" data-pltdoc="x">object%</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._define%2Fpublic%29%29" class="RktStxLink" data-pltdoc="x">define/public</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">draw</span><span class="hspace"> </span><span class="RktSym">who</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._format%29%29" class="RktValLink" data-pltdoc="x">format</a></span><span class="hspace"> </span><span class="RktVal">"reach for the sky, ~a"</span><span class="hspace"> </span><span class="RktSym">who</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="objcreation.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._super-new%29%29" class="RktStxLink" data-pltdoc="x">super-new</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">woody+c%</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._class%2Fc%29%29" class="RktStxLink" data-pltdoc="x">class/c</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">draw</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._-~3em%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>m</a></span><span class="hspace"> </span><span class="RktSym"><a href="symbols.html#%28def._%28%28quote._~23~25kernel%29._symbol~3f%29%29" class="RktValLink" data-pltdoc="x">symbol?</a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktSym">woody%</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p> </p></td></tr><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="ivaraccess.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%
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behavior of the value contained in that field when accessed from outside
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the class. Since fields may be mutated, these contracts
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are checked on any external access (via <span class="RktSym"><a href="ivaraccess.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._get-field%29%29" class="RktStxLink" data-pltdoc="x">get-field</a></span>)
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and external mutations (via <span class="RktSym"><a href="ivaraccess.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._set-field%21%29%29" class="RktStxLink" data-pltdoc="x">set-field!</a></span>) of the field.</p><p>If only the field name is present, this is equivalent to using the
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contract <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span> (but it is checked more efficiently).</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">woody/hat%</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._class%29%29" class="RktStxLink" data-pltdoc="x">class</a></span><span class="hspace"> </span><span class="RktSym">woody%</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._field%29%29" class="RktStxLink" data-pltdoc="x">field</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">hat-location</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">uninitialized</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._define%2Fpublic%29%29" class="RktStxLink" data-pltdoc="x">define/public</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">lose-hat</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="set_.html#%28form._%28%28quote._~23~25kernel%29._set%21%29%29" class="RktStxLink" data-pltdoc="x">set!</a></span><span class="hspace"> </span><span class="RktSym">hat-location</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">lost</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._define%2Fpublic%29%29" class="RktStxLink" data-pltdoc="x">define/public</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">find-hat</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="set_.html#%28form._%28%28quote._~23~25kernel%29._set%21%29%29" class="RktStxLink" data-pltdoc="x">set!</a></span><span class="hspace"> </span><span class="RktSym">hat-location</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">on-head</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="objcreation.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._super-new%29%29" class="RktStxLink" data-pltdoc="x">super-new</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">woody/hat+c%</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Object_and
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describes the expected behavior of the value paired with that name
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during class instantiation. The same name can be provided more than
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once, in which case the first such contract in the <span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._class%2Fc%29%29" class="RktStxLink" data-pltdoc="x">class/c</a></span>
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form is applied to the first value tagged with that name in the list
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of initialization arguments, and so on.</p><p>If only the initialization argument name is present, this is equivalent to using the
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contract <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span> (but it is checked more efficiently).</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">woody/init-hat%</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._class%29%29" class="RktStxLink" data-pltdoc="x">class</a></span><span class="hspace"> </span><span class="RktSym">woody%</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._init%29%29" class="RktStxLink" data-pltdoc="x">init</a></span><span class="hspace"> </span><span class="RktSym">init-hat-location</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._field%29%29" class="RktStxLink" data-pltdoc="x">field</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">hat-location</span><span class="hspace"> </span><span class="RktSym">init-hat-location</span><span class="RktPn">]</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._define%2Fpublic%29%29" class="RktStxLink" data-pltdoc="x">define/public</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">lose-hat</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="set_.html#%28form._%28%28quote._~23~25kernel%29._set%21%29%29" class="RktStxLink" data-pltdoc="x">set!</a></span><span class="hspace"> </span><span class="RktSym">hat-location</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">lost</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._define%2Fpublic%29%29" class="RktStxLink" data-pltdoc="x">define/public</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">find-hat</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="set_.html#%28form._%28%28quote._~23~25kernel%29._set%21%29%29" class="RktStxLink" data-pltdoc="x">set!</a></span><span class="hspace"> </span><span class="RktSym">hat-location</span><span class="hspace"> </span><span class="RktVal">'</span><span class="RktVal">on-head</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="objcreation.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._super-new%29%29" class="RktStxLink" data-pltdoc="x">super-new</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-
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treated as if each contract appeared in an <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._init%29%29" class="RktStxLink" data-pltdoc="x">init</a></span> section and
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a <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._field%29%29" class="RktStxLink" data-pltdoc="x">field</a></span> section.</p></li></ul><p>The internal contracts restrict the behavior of method calls
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made between classes and their subclasses; such calls are not
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controlled by the class contracts described above.</p><p>As with the external contracts, when a method or field name is specified
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but no contract appears, the contract is satisfied merely with the
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presence of the corresponding field or method.</p><ul><li><p>A method contract tagged with <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._inherit%29%29" class="RktStxLink" data-pltdoc="x">inherit</a></span> describes the
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behavior of the method when invoked directly (i.e., via
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<span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._inherit%29%29" class="RktStxLink" data-pltdoc="x">inherit</a></span>) in any subclass of the contracted class. This
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contract, like external method contracts, applies until the
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contracted class’s method implementation is no longer the entry point
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for dynamic dispatch.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="stt">> </span><span class="RktPn">(</span><span class="RktSym"><a href="objcreation.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._new%29%29" class="RktStxLink" data-pltdoc="x">new</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._class%29%29" class="RktStxLink" data-pltdoc="x">class</a></span><span class="hspace"> </span><span class="RktSym">woody+c%</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._inherit%29%29" class="RktStxLink" data-pltdoc="x">inherit</a></span><span class="hspace"> </span><span class="RktSym">draw</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="objcreation.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._super-new%29%29" class="RktStxLink" data-pltdoc="x">super-new</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._printf%29%29" class="RktValLink" data-pltdoc="x">printf</a></span><span class="hspace"> </span><span class="RktVal">"woody sez: “~a”\n"</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">draw</span><span class="hspace"> </span><span class="RktVal">"evil dr porkchop"</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><tr><td><p><span class="RktOut">woody sez: “reach for the sky, evil dr porkchop”</span></p></td></tr><tr><td><p><span class="RktRes">(object:eval:82:0 ...)</span></p></td></tr><tr><td><p> </p></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">woody+c-inherit%</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._class%2Fc%29%29" class="RktStxLink" data-pltdoc="x">class/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._inherit%29%29" class="RktStxLink" data-pltdoc="x">inherit</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">draw</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._-~3em%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>m</a></span><span class="hspace"> </span><span class="RktSym"><a href="symbols.html#%28def._%28%28quote._~23~25kernel%29._symbol~3f%29%29" class="RktValLink" data-pltdoc="x">symbol?</a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">
|
||
|
|
<span class="RktVar">method-id</span> when called by the <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._super%29%29" class="RktStxLink" data-pltdoc="x">super</a></span> form in a
|
||
|
|
subclass. This contract only affects <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._super%29%29" class="RktStxLink" data-pltdoc="x">super</a></span> calls in
|
||
|
|
subclasses which call the contract class’s implementation of
|
||
|
|
<span class="RktVar">method-id</span>.</p><p>This example shows how to extend the <span class="RktSym">draw</span> method
|
||
|
|
so that if it is passed two arguments, it combines two
|
||
|
|
calls to the original <span class="RktSym">draw</span> method, but with a
|
||
|
|
contract the controls how the <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._super%29%29" class="RktStxLink" data-pltdoc="x">super</a></span> methods must
|
||
|
|
be invoked.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">woody%+s</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._class%2Fc%29%29" class="RktStxLink" data-pltdoc="x">class/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._super%29%29" class="RktStxLink" data-pltdoc="x">super</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">draw</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._-~3em%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>m</a></span><span class="hspace"> </span><span class="RktSym"><a href="symbols.html#%28def._%28%28quote._~23~25kernel%29._symbol~3f%29%29" class="RktValLink" data-pltdoc="x">symbol?</a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._class%29%29" class="RktStxLink" data-pltdoc="x">class</a></span><span class="hspace"> </span><span class="RktSym"><a href="createclass.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._object~25%29%29" class="RktValLink" data-pltdoc="x">object%</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._define%2Fpublic%29%29" class="RktStxLink" data-pltdoc="x">define/public</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">draw</span><span class="hspace"> </span><span class="RktSym">who</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Writing.html#%28def._%28%28quote._~23~25kernel%29._format%29%29" class="RktValLink" data-pltdoc="x">format</a></span><span class="hspace"> </span><span class="RktVal">"reach for the sky, ~a"</span><span class="hspace"> </span><span class="RktSym">who</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="objcreation.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._super-new%29%29" class="RktStxLink" data-pltdoc="x">super-new</a></span><span class="RktPn">)</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span></td></tr><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29" class="RktStxLink" data-pltdoc="x">define</a></span><span class="hspace"> </span><span class="RktSym">woody2+c%</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a hr
|
||
|
|
there is no contract checking the initial <span class="RktSym">draw</span> call and
|
||
|
|
the super-call violates its contract.</p></li><li><p>A method contract tagged with <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._inner%29%29" class="RktStxLink" data-pltdoc="x">inner</a></span> describes the
|
||
|
|
behavior the class expects of an augmenting method in a subclass.
|
||
|
|
This contract affects any implementations of <span class="RktVar">method-id</span> in
|
||
|
|
subclasses which can be called via <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._inner%29%29" class="RktStxLink" data-pltdoc="x">inner</a></span> from the contracted
|
||
|
|
class. This means a subclass which implements <span class="RktVar">method-id</span> via
|
||
|
|
<span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._augment%29%29" class="RktStxLink" data-pltdoc="x">augment</a></span> or <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._overment%29%29" class="RktStxLink" data-pltdoc="x">overment</a></span> stop future subclasses from
|
||
|
|
being affected by the contract, since further extension cannot be
|
||
|
|
reached via the contracted class.</p></li><li><p>A method contract tagged with <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._override%29%29" class="RktStxLink" data-pltdoc="x">override</a></span> describes the
|
||
|
|
behavior expected by the contracted class for <span class="RktVar">method-id</span> when
|
||
|
|
called directly (i.e. by the application <span class="RktPn">(</span><span class="RktVar">method-id</span><span class="stt"> </span><span class="RktMeta"><a href="stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29._......%29%29" class="RktStxLink" data-pltdoc="x">...</a></span><span class="RktPn">)</span>).
|
||
|
|
This form can only be used if overriding the method in subclasses
|
||
|
|
will change the entry point to the dynamic dispatch chain (i.e., the
|
||
|
|
method has never been augmentable).</p><p>This time, instead of overriding <span class="RktSym">draw</span> to support
|
||
|
|
two arguments, we can make a new method, <span class="RktSym">draw2</span> that
|
||
|
|
takes the two arguments and calls <span class="RktSym">draw</span>. We also
|
||
|
|
add a contract to make sure that overriding <span class="RktSym">draw</span>
|
||
|
|
doesn’t break <span class="RktSym">draw2</span>.</p><p><div class="SIntrapara">Examples:</div><div class="SIntrapara"><blockquote class="SCodeFlow"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="attaching-contracts-to-values.html#%28form._%28%28lib._racket%2Fcontract%2Fregion..rkt%29._define%2Fcontract%29%29" class="RktStxLink" data-pltdoc="x">define/contract</a></span><span class="hspace"> </span><span class="RktSym">woody2+override/c%</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._class%2Fc%29%29" class="RktStxLink" data-pltdoc="x">class/c</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._override%29%29" class="RktStxLink" data-pltdoc="x">override</a></span><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">draw</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._-~3em%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>m</a></span><span class="hspace"> </span><span class="RktSym"><a href="symbols.html#%28def._%28%28quote._~23~25kernel%29._symbol~3f%29%29" class="RktValLink" data-pltdoc="x">symbol?</a></span><span class="hspace"> </span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string~3f%29%29" class="RktValLink" data-pltdoc="x">string?</a></span><span class="RktPn">)</span><span class="RktPn">]</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._class%29%29" class="RktStxLink" data-pltdoc="x">class</a></span><span class="hspace"> </span><span class="RktSym">woody+c%</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._inherit%29%29" class="RktStxLink" data-pltdoc="x">inherit</a></span><span class="hspace"> </span><span class="RktSym">draw</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._define%2Fpublic%29%29" class="RktStxLink" data-pltdoc="x">define/public</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">draw2</span><span class="hspace"> </span><span class="RktSym">a</span><span class="hspace"> </span><span class="RktSym">b</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="strings.html#%28def._%28%28quote._~23~25kernel%29._string-append%29%29" class="RktValLink" data-pltdoc="x">string-append</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">draw</span><span class="hspace"> </span><span class="RktSym">a</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVal">" and "</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">draw</span><span class="hspace"> 
|
||
|
|
<span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._augride%29%29" class="RktStxLink" data-pltdoc="x">augride</a></span> describes the behavior provided by the contracted
|
||
|
|
class for <span class="RktVar">method-id</span> when called directly from subclasses.
|
||
|
|
These forms can only be used if the method has previously been
|
||
|
|
augmentable, which means that no augmenting or overriding
|
||
|
|
implementation will change the entry point to the dynamic dispatch
|
||
|
|
chain. <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._augment%29%29" class="RktStxLink" data-pltdoc="x">augment</a></span> is used when subclasses can augment the
|
||
|
|
method, and <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._augride%29%29" class="RktStxLink" data-pltdoc="x">augride</a></span> is used when subclasses can override the
|
||
|
|
current augmentation.</p></li><li><p>A field contract tagged with <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._inherit-field%29%29" class="RktStxLink" data-pltdoc="x">inherit-field</a></span> describes
|
||
|
|
the behavior of the value contained in that field when accessed
|
||
|
|
directly (i.e., via <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._inherit-field%29%29" class="RktStxLink" data-pltdoc="x">inherit-field</a></span>) in any subclass of the
|
||
|
|
contracted class. Since fields may be mutated, these contracts are
|
||
|
|
checked on any access and/or mutation of the field that occurs in
|
||
|
|
such subclasses.</p></li><li><p class="SHistory">Changed in version 6.1.1.8 of package <span class="stt">base</span>: Opaque class/c now optionally ignores local
|
||
|
|
member names if an additional keyword is supplied.</p></li></ul><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/private/class-internal..rkt)._absent))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._absent%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">absent</a></span></span><span class="hspace"> </span><span class="RktVar">absent-spec</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">See <span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._class%2Fc%29%29" class="RktStxLink" data-pltdoc="x">class/c</a></span>; use outside of a <span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._class%2Fc%29%29" class="RktStxLink" data-pltdoc="x">class/c</a></span> form is a syntax error.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/class..rkt)._-~3em))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._-~3em%29%29" class="RktStxDef RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>m</a></span></span><span class="hspace"> </span><span class="RktVar">dom</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="hspace"> </span><span class="RktVar">range</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Similar to <span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span>, except that the domain of the resulting contract
|
||
|
|
contains one more element than the stated domain, where the first
|
||
|
|
(implicit) argument is contracted with <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span>. This contract is
|
||
|
|
useful for writing simpler method contracts when no properties of
|
||
|
|
<span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._this%29%29" class="RktStxLink" data-pltdoc="x">this</a></span> need to be checked.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/class..rkt)._-~3e*m))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._-~3e%2Am%29%29" class="RktStxDef RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>*m</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">mandatory-dom</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">optional-dom</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktVar">rest</span><span class="hspace"> </span><span class="RktVar">range</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Similar to <span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%2A%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>*</a></span>, except that the mandatory domain of the
|
||
|
|
resulting contract contains one more element than the stated domain,
|
||
|
|
where the first (implicit) argument is contracted with
|
||
|
|
<span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span>. This contract is useful for writing simpler method
|
||
|
|
contracts when no properties of <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._this%29%29" class="RktStxLink" data-pltdoc="x">this</a></span> need to be checked.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/class..rkt)._case-~3em))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._case-~3em%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">case->m</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">-></span><span class="hspace"> </span><span class="RktVar">dom</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="hspace"> </span><span class="RktVar">rest</span><span class="hspace"> </span><span class="RktVar">range</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Similar to <span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._case-~3e%29%29" class="RktStxLink" data-pltdoc="x">case-></a></span>, except that the mandatory domain of each
|
||
|
|
case of the resulting contract contains one more element than the stated
|
||
|
|
domain, where the first (implicit) argument is contracted with
|
||
|
|
<span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span>. This contract is useful for writing simpler method
|
||
|
|
contracts when no properties of <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._this%29%29" class="RktStxLink" data-pltdoc="x">this</a></span> need to be checked.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><table cellspacing="0" cellpadding="0" class="RktBlk RForeground"><tr><td><span class="RktPn">(</span><a name="(form._((lib._racket/class..rkt)._-~3edm))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._-~3edm%29%29" class="RktStxDef RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>dm</a></span></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">mandatory-dependent-dom</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">optional-dependent-dom</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">dependent-rest</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">pre-cond</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">dep-range</span><span class="RktPn">)</span></td></tr></table></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">Similar to <span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3ed%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>d</a></span>, except that the mandatory domain of the resulting contract
|
||
|
|
contains one more element than the stated domain, where the first (implicit) argument is contracted
|
||
|
|
with <span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fmisc..rkt%29._any%2Fc%29%29" class="RktValLink" data-pltdoc="x">any/c</a></span>. In addition, <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._this%29%29" class="RktStxLink" data-pltdoc="x">this</a></span> is appropriately bound in the body of the contract.
|
||
|
|
This contract is useful for writing simpler method contracts when no properties
|
||
|
|
of <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._this%29%29" class="RktStxLink" data-pltdoc="x">this</a></span> need to be checked.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/class..rkt)._object/c))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._object%2Fc%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">object/c</a></span></span><span class="hspace"> </span><span class="RktVar">member-spec</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">member-spec</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">method-spec</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._field%29%29" class="RktStxLink" data-pltdoc="x">field</a></span><span class="hspace"> </span><span class="RktVar">field-spec</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">method-spec</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">method-id</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktVar">method-id</span><span class="hspace"> </span><span class="RktVar">method-contract</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">field-spec</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktVar">field-id</span></td></tr><tr><td align="ri
|
||
|
|
<span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._class%2Fc%29%29" class="RktStxLink" data-pltdoc="x">class/c</a></span>, arbitrary contract expressions are allowed.
|
||
|
|
Also, method contracts for <span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._object%2Fc%29%29" class="RktStxLink" data-pltdoc="x">object/c</a></span> follow those for
|
||
|
|
<span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._class%2Fc%29%29" class="RktStxLink" data-pltdoc="x">class/c</a></span>. An object wrapped with <span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._object%2Fc%29%29" class="RktStxLink" data-pltdoc="x">object/c</a></span>
|
||
|
|
behaves as if its class had been wrapped with the equivalent
|
||
|
|
<span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._class%2Fc%29%29" class="RktStxLink" data-pltdoc="x">class/c</a></span> contract.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/class..rkt)._instanceof/c))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28def._%28%28lib._racket%2Fclass..rkt%29._instanceof%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">instanceof/c</a></span></span><span class="hspace"> </span><span class="RktVar">class-contract</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">class-contract</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Produces a contract for an object, where the object is an
|
||
|
|
instance of a class that conforms to <span class="RktVar">class-contract</span>.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><table cellspacing="0" cellpadding="0" class="prototype RForeground"><tr><td valign="top"><span class="RktPn">(</span><a name="(def._((lib._racket/class..rkt)._dynamic-object/c))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28def._%28%28lib._racket%2Fclass..rkt%29._dynamic-object%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">dynamic-object/c</a></span></span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">method-names</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">method-contracts</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">field-names</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td></tr><tr><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktVar">field-contracts</span><span class="RktPn">)</span></td><td valign="top"><span class="hspace"> </span></td><td valign="top">→</td><td valign="top"><span class="hspace"> </span></td><td valign="top"><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></td></tr></table></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">method-names</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._listof%29%29" class="RktValLink" data-pltdoc="x">listof</a></span><span class="hspace"> </span><span class="RktSym"><a href="symbols.html#%28def._%28%28quote._~23~25kernel%29._symbol~3f%29%29" class="RktValLink" data-pltdoc="x">symbol?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">method-contracts</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._listof%29%29" class="RktValLink" data-pltdoc="x">listof</a></span><span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">field-names</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._listo
|
||
|
|
where the names and contracts for both methods and fields can be
|
||
|
|
computed dynamically. The list of names and contracts for both
|
||
|
|
methods and field respectively must have the same lengths.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>syntax</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(form._((lib._racket/class..rkt)._object-contract))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._object-contract%29%29" class="RktStxDef RktStxLink" data-pltdoc="x">object-contract</a></span></span><span class="hspace"> </span><span class="RktVar">member-spec</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span></p></blockquote></td></tr><tr><td><span class="stt"> </span></td></tr><tr><td><table cellspacing="0" cellpadding="0" class="specgrammar"><tr><td align="right" valign="baseline"><span class="RktVar">member-spec</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktVar">method-id</span><span class="hspace"> </span><span class="RktVar">method-contract</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._field%29%29" class="RktStxLink" data-pltdoc="x">field</a></span><span class="hspace"> </span><span class="RktVar">field-id</span><span class="hspace"> </span><span class="RktVar">contract-expr</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td></tr><tr><td align="right" valign="baseline"><span class="RktVar">method-contract</span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">=</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span></a></span><span class="hspace"> </span><span class="RktVar">dom</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="hspace"> </span><span class="RktVar">range</span><span class="RktPn">)</span></td></tr><tr><td align="right" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="center" valign="baseline">|</td><td align="left" valign="baseline"><span class="stt"> </span></td><td align="left" valign="baseline"><table cellspacing="0" cellpadding="0" class="RktBlk"><tr><td><span class="RktPn">(</span><span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3e%2A%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>*</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktVar">mandatory-dom</span><span class="hspace"> </span><span class="RktMeta">...</span><span cla
|
||
|
|
the corresponding function contract, but the syntax of the
|
||
|
|
method contract must be written directly in the body of the
|
||
|
|
object-contract—<wbr></wbr>much like the way that methods in class
|
||
|
|
definitions use the same syntax as regular function
|
||
|
|
definitions, but cannot be arbitrary procedures. Unlike the
|
||
|
|
method contracts for <span class="RktSym"><a href="Object_and_Class_Contracts.html#%28form._%28%28lib._racket%2Fclass..rkt%29._class%2Fc%29%29" class="RktStxLink" data-pltdoc="x">class/c</a></span>, the implicit <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._this%29%29" class="RktStxLink" data-pltdoc="x">this</a></span>
|
||
|
|
argument is not part of the contract. To allow for the use of
|
||
|
|
<span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._this%29%29" class="RktStxLink" data-pltdoc="x">this</a></span> in dependent contracts, <span class="RktSym"><a href="function-contracts.html#%28form._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._-~3ed%29%29" class="RktStxLink" data-pltdoc="x"><span class="nobreak">-></span>d</a></span> contracts
|
||
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implicitly bind <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._this%29%29" class="RktStxLink" data-pltdoc="x">this</a></span> to the object itself.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>value</p></div></div><p class="RForeground"><a name="(def._((lib._racket/class..rkt)._mixin-contract))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28def._%28%28lib._racket%2Fclass..rkt%29._mixin-contract%29%29" class="RktValDef RktValLink" data-pltdoc="x">mixin-contract</a></span></span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr></table></blockquote></div><div class="SIntrapara">A <a href="function-contracts.html#%28tech._function._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">function contract</span></a> that recognizes mixins. It guarantees that
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the input to the function is a class and the result of the function is
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a subclass of the input.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/class..rkt)._make-mixin-contract))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28def._%28%28lib._racket%2Fclass..rkt%29._make-mixin-contract%29%29" class="RktValDef RktValLink" data-pltdoc="x">make-mixin-contract</a></span></span><span class="hspace"> </span><span class="RktVar">type</span><span class="hspace"> </span><span class="RktMeta">...</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._contract~3f%29%29" class="RktValLink" data-pltdoc="x">contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">type</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="objectutils.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._class~3f%29%29" class="RktValLink" data-pltdoc="x">class?</a></span><span class="hspace"> </span><span class="RktSym"><a href="objectutils.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._interface~3f%29%29" class="RktValLink" data-pltdoc="x">interface?</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Produces a <a href="function-contracts.html#%28tech._function._contract%29" class="techoutside" data-pltdoc="x"><span class="techinside">function contract</span></a> that guarantees the input to the
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function is a class that implements/subclasses each <span class="RktVar">type</span>, and
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that the result of the function is a subclass of the input.</div></p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/class..rkt)._is-a~3f/c))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28def._%28%28lib._racket%2Fclass..rkt%29._is-a~3f%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">is-a?/c</a></span></span><span class="hspace"> </span><span class="RktVar">type</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">type</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="data-structure-contracts.html#%28def._%28%28lib._racket%2Fcontract%2Fbase..rkt%29._or%2Fc%29%29" class="RktValLink" data-pltdoc="x">or/c</a></span><span class="hspace"> </span><span class="RktSym"><a href="objectutils.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._class~3f%29%29" class="RktValLink" data-pltdoc="x">class?</a></span><span class="hspace"> </span><span class="RktSym"><a href="objectutils.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._interface~3f%29%29" class="RktValLink" data-pltdoc="x">interface?</a></span><span class="RktPn">)</span></td></tr></table></blockquote></div><div class="SIntrapara">Accepts a class or interface and returns a flat contract that
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recognizes objects that instantiate the class/interface.</div></p><p>See <span class="RktSym"><a href="objectutils.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._is-a~3f%29%29" class="RktValLink" data-pltdoc="x">is-a?</a></span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/class..rkt)._implementation~3f/c))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28def._%28%28lib._racket%2Fclass..rkt%29._implementation~3f%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">implementation?/c</a></span></span><span class="hspace"> </span><span class="RktVar">interface</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">interface</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="objectutils.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._interface~3f%29%29" class="RktValLink" data-pltdoc="x">interface?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a flat contract that recognizes classes that implement
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<span class="RktVar">interface</span>.</div></p><p>See <span class="RktSym"><a href="objectutils.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._implementation~3f%29%29" class="RktValLink" data-pltdoc="x">implementation?</a></span>.</p><p><div class="SIntrapara"><blockquote class="SVInsetFlow"><table cellspacing="0" cellpadding="0" class="boxed RBoxed"><tr><td><blockquote class="SubFlow"><div class="RBackgroundLabel SIEHidden"><div class="RBackgroundLabelInner"><p>procedure</p></div></div><p class="RForeground"><span class="RktPn">(</span><a name="(def._((lib._racket/class..rkt)._subclass~3f/c))"></a><span title="Provided from: racket/class, racket | Package: base"><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28def._%28%28lib._racket%2Fclass..rkt%29._subclass~3f%2Fc%29%29" class="RktValDef RktValLink" data-pltdoc="x">subclass?/c</a></span></span><span class="hspace"> </span><span class="RktVar">class</span><span class="RktPn">)</span><span class="hspace"> </span>→<span class="hspace"> </span><span class="RktSym"><a href="contract-utilities.html#%28def._%28%28lib._racket%2Fcontract%2Fprivate%2Fguts..rkt%29._flat-contract~3f%29%29" class="RktValLink" data-pltdoc="x">flat-contract?</a></span></p></blockquote></td></tr><tr><td><span class="hspace"> </span><span class="RktVar">class</span><span class="hspace"> </span>:<span class="hspace"> </span><span class="RktSym"><a href="objectutils.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._class~3f%29%29" class="RktValLink" data-pltdoc="x">class?</a></span></td></tr></table></blockquote></div><div class="SIntrapara">Returns a flat contract that recognizes classes that
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are subclasses of <span class="RktVar">class</span>.</div></p><p>See <span class="RktSym"><a href="objectutils.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._subclass~3f%29%29" class="RktValLink" data-pltdoc="x">subclass?</a></span>.</p><div class="navsetbottom"><span class="navleft"><form class="searchform"><input class="searchbox" id="searchbox" type="text" tabindex="1" placeholder="...search manuals..." title="Enter a search string to search the manuals" onkeypress="return DoSearchKey(event, this, "8.6", "../");"/></form> <a href="https://docs.racket-lang.org/index.html" title="up to the documentation top" data-pltdoc="x" onclick="return GotoPLTRoot("8.6");">top</a><span class="tocsettoggle"> <a href="javascript:void(0);" title="show/hide table of contents" onclick="TocsetToggle();">contents</a></span></span><span class="navright"> <a href="trait.html" title="backward to "6.6 Traits"" data-pltdoc="x">← prev</a> <a href="mzlib_class.html" title="up to "6 Classes and Objects"" data-pltdoc="x">up</a> <a href="objectequality.html" title="forward to "6.8 Object Equality and Hashing"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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