116 lines
4.9 KiB
HTML
116 lines
4.9 KiB
HTML
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<!DOCTYPE html>
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<html>
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<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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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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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
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copy of the license is included in the section entitled "GNU Free
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Documentation License." -->
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<title>Next-method (Guile Reference Manual)</title>
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<meta name="description" content="Next-method (Guile Reference Manual)">
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<meta name="keywords" content="Next-method (Guile Reference Manual)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content=".texi2any-real">
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<meta name="viewport" content="width=device-width,initial-scale=1">
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<link href="index.html" rel="start" title="Top">
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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="Methods-and-Generic-Functions.html" rel="up" title="Methods and Generic Functions">
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<link href="Generic-Function-and-Method-Examples.html" rel="next" title="Generic Function and Method Examples">
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<link href="Merging-Generics.html" rel="prev" title="Merging Generics">
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</style>
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<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="Next_002dmethod">
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<div class="nav-panel">
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<p>
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Next: <a href="Generic-Function-and-Method-Examples.html" accesskey="n" rel="next">Generic Function and Method Examples</a>, Previous: <a href="Merging-Generics.html" accesskey="p" rel="prev">Merging Generics</a>, Up: <a href="Methods-and-Generic-Functions.html" accesskey="u" rel="up">Methods and Generic Functions</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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</div>
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<hr>
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<h4 class="subsection" id="Next_002dmethod-1"><span>8.6.4 Next-method<a class="copiable-link" href="#Next_002dmethod-1"> ¶</a></span></h4>
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<p>When you call a generic function, with a particular set of arguments,
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GOOPS builds a list of all the methods that are applicable to those
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arguments and orders them by how closely the method definitions match
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the actual argument types. It then calls the method at the top of this
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list. If the selected method’s code wants to call on to the next method
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in this list, it can do so by using <code class="code">next-method</code>.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(define-method (Test (a <integer>)) (cons 'integer (next-method)))
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(define-method (Test (a <number>)) (cons 'number (next-method)))
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(define-method (Test a) (list 'top))
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</pre></div>
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<p>With these definitions,
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(Test 1) ⇒ (integer number top)
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(Test 1.0) ⇒ (number top)
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(Test #t) ⇒ (top)
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</pre></div>
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<p><code class="code">next-method</code> is always called as just <code class="code">(next-method)</code>. The
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arguments for the next method call are always implicit, and always the
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same as for the original method call.
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</p>
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<p>If you want to call on to a method with the same name but with a
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different set of arguments (as you might with overloaded methods in C++,
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for example), you do not use <code class="code">next-method</code>, but instead simply
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write the new call as usual:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(define-method (Test (a <number>) min max)
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(if (and (>= a min) (<= a max))
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(display "Number is in range\n"))
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(Test a))
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(Test 2 1 10)
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-|
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Number is in range
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⇒
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(integer number top)
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</pre></div>
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<p>(You should be careful in this case that the <code class="code">Test</code> calls do not
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lead to an infinite recursion, but this consideration is just the same
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as in Scheme code in general.)
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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="Generic-Function-and-Method-Examples.html">Generic Function and Method Examples</a>, Previous: <a href="Merging-Generics.html">Merging Generics</a>, Up: <a href="Methods-and-Generic-Functions.html">Methods and Generic Functions</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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</div>
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</body>
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</html>
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