127 lines
5.5 KiB
HTML
127 lines
5.5 KiB
HTML
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<!-- This manual documents Guile version 3.0.10.
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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>Inheritance (Guile Reference Manual)</title>
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="GOOPS.html" rel="up" title="GOOPS">
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<body lang="en">
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<div class="section-level-extent" id="Inheritance">
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<div class="nav-panel">
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<p>
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Next: <a href="Introspection.html" accesskey="n" rel="next">Introspection</a>, Previous: <a href="Methods-and-Generic-Functions.html" accesskey="p" rel="prev">Methods and Generic Functions</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="Inheritance-1"><span>8.7 Inheritance<a class="copiable-link" href="#Inheritance-1"> ¶</a></span></h3>
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<p>Here are some class definitions to help illustrate inheritance:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(define-class A () a)
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(define-class B () b)
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(define-class C () c)
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(define-class D (A B) d a)
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(define-class E (A C) e c)
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(define-class F (D E) f)
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</pre></div>
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<p><code class="code">A</code>, <code class="code">B</code>, <code class="code">C</code> have a null list of superclasses. In this
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case, the system will replace the null list by a list which only
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contains <code class="code"><object></code>, the root of all the classes defined by
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<code class="code">define-class</code>. <code class="code">D</code>, <code class="code">E</code>, <code class="code">F</code> use multiple
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inheritance: each class inherits from two previously defined classes.
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Those class definitions define a hierarchy which is shown in
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<a class="ref" href="#fig_003ahier">Figure 8.2</a>. In this figure, the class <code class="code"><top></code> is also shown;
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this class is the superclass of all Scheme objects. In particular,
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<code class="code"><top></code> is the superclass of all standard Scheme
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types.
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</p>
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<div class="float" id="fig_003ahier">
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<pre class="verbatim"> <top>
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/ \\\_____________________
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/ \\___________ \
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/ \ \ \
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<object> <pair> <procedure> <number>
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/ | \ |
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/ | \ |
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A B C <complex>
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|\__/__ | |
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\ / \ / |
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D E <real>
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\ / |
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F |
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<integer>
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</pre>
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<div class="caption"><p><strong class="strong">Figure 8.2: </strong>A class hierarchy.</p></div></div>
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<p>When a class has superclasses, its set of slots is calculated by taking
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the union of its own slots and those of all its superclasses. Thus each
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instance of D will have three slots, <code class="code">a</code>, <code class="code">b</code> and
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<code class="code">d</code>). The slots of a class can be discovered using the
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<code class="code">class-slots</code> primitive. For instance,
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(class-slots A) ⇒ ((a))
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(class-slots E) ⇒ ((a) (e) (c))
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(class-slots F) ⇒ ((e) (c) (b) (d) (a) (f))
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</pre></div>
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<p>The ordering of the returned slots is not significant.
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</p>
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<ul class="mini-toc">
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<li><a href="Class-Precedence-List.html" accesskey="1">Class Precedence List</a></li>
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<li><a href="Sorting-Methods.html" accesskey="2">Sorting Methods</a></li>
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</ul>
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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="Introspection.html">Introspection</a>, Previous: <a href="Methods-and-Generic-Functions.html">Methods and Generic Functions</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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