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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>6.1 Creating Interfaces</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="icons.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
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<span class="RktSym"><a href="createinterface.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._interface%29%29" class="RktStxLink" data-pltdoc="x">interface</a></span> expression is evaluated. The result of each
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<span class="RktVar">super-interface-expr</span> must be an interface value, otherwise
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the <span class="RktSym"><a href="objectutils.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._exn~3afail~3aobject%29%29" class="RktValLink" data-pltdoc="x">exn:fail:object</a></span> exception is raised. The interfaces returned by the
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<span class="RktVar">super-interface-expr</span>s are the new interface’s
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superinterfaces, which are all extended by the new interface. Any
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class that implements the new interface also implements all of the
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superinterfaces.</p><p>The result of an <span class="RktSym"><a href="createinterface.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._interface%29%29" class="RktStxLink" data-pltdoc="x">interface</a></span> expression is an interface that
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includes all of the specified <span class="RktVar">id</span>s, plus all identifiers from
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the superinterfaces. Duplicate identifier names among the
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superinterfaces are ignored, but if a superinterface contains one of
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the <span class="RktVar">id</span>s in the <span class="RktSym"><a href="createinterface.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._interface%29%29" class="RktStxLink" data-pltdoc="x">interface</a></span> expression, the
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<span class="RktSym"><a href="objectutils.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._exn~3afail~3aobject%29%29" class="RktValLink" data-pltdoc="x">exn:fail:object</a></span> exception is raised. A given <span class="RktVar">id</span> may be paired with
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a corresponding <span class="RktVar">contract-expr</span>.</p><p>If no <span class="RktVar">super-interface-expr</span>s are provided, then the derivation
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requirement of the resulting interface is trivial: any class that
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implements the interface must be derived from <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>.
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Otherwise, the implementation requirement of the resulting interface
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is the most specific requirement from its superinterfaces. If the
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superinterfaces specify inconsistent derivation requirements, the
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<span class="RktSym"><a href="objectutils.html#%28def._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._exn~3afail~3aobject%29%29" class="RktValLink" data-pltdoc="x">exn:fail:object</a></span> exception is raised.</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">file-interface<%></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createinterface.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._interface%29%29" class="RktStxLink" data-pltdoc="x">interface</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktSym"><a href="creatingunits.html#%28form._%28%28lib._racket%2Funit..rkt%29._open%29%29" class="RktStxLink" data-pltdoc="x">open</a></span><span class="hspace"> </span><span class="RktSym">close</span><span class="hspace"> </span><span class="RktSym"><a href="Byte_and_String_Input.html#%28def._%28%28quote._~23~25kernel%29._read-byte%29%29" class="RktValLink" data-pltdoc="x">read-byte</a></span><span class="hspace"> </span><span class="RktSym"><a href="Byte_and_String_Output.html#%28def._%28%28quote._~23~25kernel%29._write-byte%29%29" class="RktValLink" data-pltdoc="x">write-byte</a></span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr><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">directory-interface<%></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createinterface.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._interface%29%29" class="RktStxLink" data-pltdoc="x">interface</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">file-interface<%></span><span class="RktPn">)</span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">[</span><span class="RktSym">file-list</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="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="RktPn">(</span><span class="RktSym"><a href="Object_and_Class_Contracts.html#%28def._%28%28lib._racket%2Fclass..rkt%29._is-a~3f%2Fc%29%29" class="RktValLink" data-pltdoc="x">is-a?/c</a></span><span class="hspace"> </span><span class="RktSym">file-interface<%></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="RktSym">parent-directory</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr></table></blockquote></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="R
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structure-type properties produced by the <span class="RktVar">property-expr</span>s with
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the corresponding <span class="RktVar">val-expr</span>s.</div></p><p>Whenever the resulting interface (or a sub-interface derived from it)
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is explicitly implemented by a class through the <span class="RktSym"><a href="createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._class%2A%29%29" class="RktStxLink" data-pltdoc="x">class*</a></span> form,
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each property is attached with its value to a structure type that
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instantiated by instances of the class. Specifically, the property is
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attached to a structure type with zero immediate fields, which is
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extended to produce the internal structure type for instances of the
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class (so that no information about fields is accessible to the
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structure type property’s guard, if any).</p><p><div class="SIntrapara">Example:</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">i<%></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="createinterface.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._interface%2A%29%29" class="RktStxLink" data-pltdoc="x">interface*</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktPn">[</span><span class="RktSym"><a href="Printer_Extension.html#%28def._%28%28quote._~23~25kernel%29._prop~3acustom-write%29%29" class="RktValLink" data-pltdoc="x">prop:custom-write</a></span></td></tr><tr><td><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="lambda.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._lambda%29%29" class="RktStxLink" data-pltdoc="x">lambda</a></span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym">obj</span><span class="hspace"> </span><span class="RktSym">port</span><span class="hspace"> </span><span class="RktSym">mode</span><span class="RktPn">)</span><span class="hspace"> </span><span class="RktPn">(</span><span class="RktSym"><a href="void.html#%28def._%28%28quote._~23~25kernel%29._void%29%29" class="RktValLink" data-pltdoc="x">void</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="RktSym">method1</span><span class="hspace"> </span><span class="RktSym">method2</span><span class="hspace"> </span><span class="RktSym">method3</span><span class="RktPn">)</span><span class="RktPn">)</span></td></tr></table></td></tr></table></blockquote></div></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="mzlib_class.html" title="backward to "6 Classes and Objects"" data-pltdoc="x">← prev</a> <a href="mzlib_class.html" title="up to "6 Classes and Objects"" data-pltdoc="x">up</a> <a href="createclass.html" title="forward to "6.2 Creating Classes"" data-pltdoc="x">next →</a></span> </div></div></div><div id="contextindicator"> </div></body></html>
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