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138 lines
7.8 KiB
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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<title>GOOPS Object Miscellany (Guile Reference Manual)</title>
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<div class="section-level-extent" id="GOOPS-Object-Miscellany">
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Next: <a href="The-Metaobject-Protocol.html" accesskey="n" rel="next">The Metaobject Protocol</a>, Previous: <a href="GOOPS-Error-Handling.html" accesskey="p" rel="prev">Error Handling</a>, Up: <a href="GOOPS.html" accesskey="u" rel="up">GOOPS</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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<h3 class="section" id="GOOPS-Object-Miscellany-1"><span>8.10 GOOPS Object Miscellany<a class="copiable-link" href="#GOOPS-Object-Miscellany-1"> ¶</a></span></h3>
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<p>Here we cover some points about GOOPS objects that aren’t substantial
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enough to merit sections on their own.
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</p>
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<h4 class="subheading" id="Object-Equality"><span>Object Equality<a class="copiable-link" href="#Object-Equality"> ¶</a></span></h4>
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<p>When GOOPS is loaded, <code class="code">eqv?</code>, <code class="code">equal?</code> and <code class="code">=</code> become
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generic functions, and you can define methods for them, specialized for
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your own classes, so as to control what the various kinds of equality
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mean for your classes.
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</p>
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<p>For example, the <code class="code">assoc</code> procedure, for looking up an entry in an
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alist, is specified as using <code class="code">equal?</code> to determine when the car of
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an entry in the alist is the same as the key parameter that <code class="code">assoc</code>
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is called with. Hence, if you had defined a new class, and wanted to
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use instances of that class as the keys in an alist, you could define a
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method for <code class="code">equal?</code>, for your class, to control <code class="code">assoc</code>’s
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lookup precisely.
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</p>
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<h4 class="subheading" id="Cloning-Objects"><span>Cloning Objects<a class="copiable-link" href="#Cloning-Objects"> ¶</a></span></h4>
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<dl class="first-deffn">
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<dt class="deffn" id="index-shallow_002dclone"><span class="category-def">generic: </span><span><strong class="def-name">shallow-clone</strong><a class="copiable-link" href="#index-shallow_002dclone"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-shallow_002dclone-1"><span class="category-def">method: </span><span><strong class="def-name">shallow-clone</strong> <var class="def-var-arguments">(self <object>)</var><a class="copiable-link" href="#index-shallow_002dclone-1"> ¶</a></span></dt>
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<dd><p>Return a “shallow” clone of <var class="var">self</var>. The default method makes a
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shallow clone by allocating a new instance and copying slot values from
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self to the new instance. Each slot value is copied either as an
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immediate value or by reference.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-deep_002dclone"><span class="category-def">generic: </span><span><strong class="def-name">deep-clone</strong><a class="copiable-link" href="#index-deep_002dclone"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-deep_002dclone-1"><span class="category-def">method: </span><span><strong class="def-name">deep-clone</strong> <var class="def-var-arguments">(self <object>)</var><a class="copiable-link" href="#index-deep_002dclone-1"> ¶</a></span></dt>
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<dd><p>Return a “deep” clone of <var class="var">self</var>. The default method makes a deep
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clone by allocating a new instance and copying or cloning slot values
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from self to the new instance. If a slot value is an instance
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(satisfies <code class="code">instance?</code>), it is cloned by calling <code class="code">deep-clone</code>
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on that value. Other slot values are copied either as immediate values
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or by reference.
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</p></dd></dl>
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<h4 class="subheading" id="Write-and-Display"><span>Write and Display<a class="copiable-link" href="#Write-and-Display"> ¶</a></span></h4>
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<dl class="first-deffn">
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<dt class="deffn" id="index-write-3"><span class="category-def">primitive generic: </span><span><strong class="def-name">write</strong> <var class="def-var-arguments">object port</var><a class="copiable-link" href="#index-write-3"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-display-3"><span class="category-def">primitive generic: </span><span><strong class="def-name">display</strong> <var class="def-var-arguments">object port</var><a class="copiable-link" href="#index-display-3"> ¶</a></span></dt>
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<dd><p>When GOOPS is loaded, <code class="code">write</code> and <code class="code">display</code> become generic
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functions with special methods for printing
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</p>
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<ul class="itemize mark-bullet">
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<li>objects - instances of the class <code class="code"><object></code>
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</li><li>foreign objects - instances of the class <code class="code"><foreign-object></code>
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</li><li>classes - instances of the class <code class="code"><class></code>
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</li><li>generic functions - instances of the class <code class="code"><generic></code>
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</li><li>methods - instances of the class <code class="code"><method></code>.
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</li></ul>
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<p><code class="code">write</code> and <code class="code">display</code> print non-GOOPS values in the same way
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as the Guile primitive <code class="code">write</code> and <code class="code">display</code> functions.
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</p></dd></dl>
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<p>In addition to the cases mentioned, you can of course define
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<code class="code">write</code> and <code class="code">display</code> methods for your own classes, to
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customize how instances of those classes are printed.
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</p>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Next: <a href="The-Metaobject-Protocol.html">The Metaobject Protocol</a>, Previous: <a href="GOOPS-Error-Handling.html">Error Handling</a>, Up: <a href="GOOPS.html">GOOPS</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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