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140 lines
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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>Instance Creation (Guile Reference Manual)</title>
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<div class="section-level-extent" id="Instance-Creation">
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<p>
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Next: <a href="Slot-Options.html" accesskey="n" rel="next">Slot Options</a>, Previous: <a href="Class-Definition.html" accesskey="p" rel="prev">Class Definition</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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<hr>
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<h3 class="section" id="Instance-Creation-and-Slot-Access"><span>8.3 Instance Creation and Slot Access<a class="copiable-link" href="#Instance-Creation-and-Slot-Access"> ¶</a></span></h3>
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<p>An instance (or object) of a defined class can be created with
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<code class="code">make</code>. <code class="code">make</code> takes one mandatory parameter, which is the
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class of the instance to create, and a list of optional arguments that
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will be used to initialize the slots of the new instance. For instance
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the following form
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</p>
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<a class="index-entry-id" id="index-make"></a>
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<a class="index-entry-id" id="index-instance"></a>
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<div class="example lisp">
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<pre class="lisp-preformatted">(define c (make <my-complex>))
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</pre></div>
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<p>creates a new <code class="code"><my-complex></code> object and binds it to the Scheme
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variable <code class="code">c</code>.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-make-1"><span class="category-def">generic: </span><span><strong class="def-name">make</strong><a class="copiable-link" href="#index-make-1"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-make-2"><span class="category-def">method: </span><span><strong class="def-name">make</strong> <var class="def-var-arguments">(class <class>) initarg …</var><a class="copiable-link" href="#index-make-2"> ¶</a></span></dt>
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<dd><p>Create and return a new instance of class <var class="var">class</var>, initialized using
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<var class="var">initarg</var> <small class="enddots">...</small>.
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</p>
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<p>In theory, <var class="var">initarg</var> … can have any structure that is
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understood by whatever methods get applied when the <code class="code">initialize</code>
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generic function is applied to the newly allocated instance.
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</p>
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<p>In practice, specialized <code class="code">initialize</code> methods would normally call
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<code class="code">(next-method)</code>, and so eventually the standard GOOPS
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<code class="code">initialize</code> methods are applied. These methods expect
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<var class="var">initargs</var> to be a list with an even number of elements, where
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even-numbered elements (counting from zero) are keywords and
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odd-numbered elements are the corresponding values.
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</p>
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<p>GOOPS processes initialization argument keywords automatically for slots
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whose definition includes the <code class="code">#:init-keyword</code> option (see <a class="pxref" href="Slot-Options.html">init-keyword</a>). Other keyword value pairs can only be
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processed by an <code class="code">initialize</code> method that is specialized for the new
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instance’s class. Any unprocessed keyword value pairs are ignored.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-make_002dinstance"><span class="category-def">generic: </span><span><strong class="def-name">make-instance</strong><a class="copiable-link" href="#index-make_002dinstance"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-make_002dinstance-1"><span class="category-def">method: </span><span><strong class="def-name">make-instance</strong> <var class="def-var-arguments">(class <class>) initarg …</var><a class="copiable-link" href="#index-make_002dinstance-1"> ¶</a></span></dt>
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<dd><p><code class="code">make-instance</code> is an alias for <code class="code">make</code>.
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</p></dd></dl>
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<p>The slots of the new complex number can be accessed using
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<code class="code">slot-ref</code> and <code class="code">slot-set!</code>. <code class="code">slot-set!</code> sets the value
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of an object slot and <code class="code">slot-ref</code> retrieves it.
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</p>
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<a class="index-entry-id" id="index-slot_002dset_0021"></a>
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<a class="index-entry-id" id="index-slot_002dref"></a>
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<div class="example lisp">
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<div class="group"><pre class="lisp-preformatted">(slot-set! c 'r 10)
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(slot-set! c 'i 3)
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(slot-ref c 'r) ⇒ 10
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(slot-ref c 'i) ⇒ 3
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</pre></div></div>
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<p>The <code class="code">(oop goops describe)</code> module provides a <code class="code">describe</code>
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function that is useful for seeing all the slots of an object; it prints
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the slots and their values to standard output.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(describe c)
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-|
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#<<my-complex> 401d8638> is an instance of class <my-complex>
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Slots are:
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r = 10
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i = 3
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</pre></div>
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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="Slot-Options.html">Slot Options</a>, Previous: <a href="Class-Definition.html">Class Definition</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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