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97 lines
4.3 KiB
HTML
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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<title>MOP Specification (Guile Reference Manual)</title>
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<div class="subsection-level-extent" id="MOP-Specification">
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Next: <a href="Instance-Creation-Protocol.html" accesskey="n" rel="next">Instance Creation Protocol</a>, Previous: <a href="Metaclasses.html" accesskey="p" rel="prev">Metaclasses</a>, Up: <a href="The-Metaobject-Protocol.html" accesskey="u" rel="up">The Metaobject Protocol</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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<h4 class="subsection" id="MOP-Specification-1"><span>8.11.3 MOP Specification<a class="copiable-link" href="#MOP-Specification-1"> ¶</a></span></h4>
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<p>The aim of the MOP specification in this chapter is to specify all the
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customizable generic function invocations that can be made by the standard
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GOOPS syntax, procedures and methods, and to explain the protocol for
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customizing such invocations.
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</p>
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<p>A generic function invocation is customizable if the types of the
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arguments to which it is applied are not completely determined by the
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lexical context in which the invocation appears. For example, the
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<code class="code">(initialize <var class="var">instance</var> <var class="var">initargs</var>)</code> invocation in the
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default <code class="code">make-instance</code> method is customizable, because the type of
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the <code class="code"><var class="var">instance</var></code> argument is determined by the class that was
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passed to <code class="code">make-instance</code>.
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</p>
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<p>(Whereas — to give a counter-example — the <code class="code">(make <generic>
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#:name ',name)</code> invocation in <code class="code">define-generic</code> is not customizable,
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because all of its arguments have lexically determined types.)
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</p>
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<p>When using this rule to decide whether a given generic function invocation
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is customizable, we ignore arguments that are expected to be handled in
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method definitions as a single “rest” list argument.
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</p>
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<p>For each customizable generic function invocation, the <em class="dfn">invocation
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protocol</em> is explained by specifying
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</p>
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<ul class="itemize mark-bullet">
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<li>what, conceptually, the applied method is intended to do
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</li><li>what assumptions, if any, the caller makes about the applied method’s side
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effects
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</li><li>what the caller expects to get as the applied method’s return value.
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</li></ul>
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