115 lines
4.9 KiB
HTML
115 lines
4.9 KiB
HTML
<!DOCTYPE html>
|
|
<html>
|
|
<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<!-- This manual documents Guile version 3.0.10.
|
|
|
|
Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
|
|
Inc.
|
|
|
|
Copyright (C) 2021 Maxime Devos
|
|
|
|
Copyright (C) 2024 Tomas Volf
|
|
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
|
any later version published by the Free Software Foundation; with no
|
|
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
|
|
copy of the license is included in the section entitled "GNU Free
|
|
Documentation License." -->
|
|
<title>Next-method (Guile Reference Manual)</title>
|
|
|
|
<meta name="description" content="Next-method (Guile Reference Manual)">
|
|
<meta name="keywords" content="Next-method (Guile Reference Manual)">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content=".texi2any-real">
|
|
<meta name="viewport" content="width=device-width,initial-scale=1">
|
|
|
|
<link href="index.html" rel="start" title="Top">
|
|
<link href="Concept-Index.html" rel="index" title="Concept Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="Methods-and-Generic-Functions.html" rel="up" title="Methods and Generic Functions">
|
|
<link href="Generic-Function-and-Method-Examples.html" rel="next" title="Generic Function and Method Examples">
|
|
<link href="Merging-Generics.html" rel="prev" title="Merging Generics">
|
|
<style type="text/css">
|
|
<!--
|
|
a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em}
|
|
div.example {margin-left: 3.2em}
|
|
span:hover a.copiable-link {visibility: visible}
|
|
-->
|
|
</style>
|
|
<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<div class="subsection-level-extent" id="Next_002dmethod">
|
|
<div class="nav-panel">
|
|
<p>
|
|
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>
|
|
</div>
|
|
<hr>
|
|
<h4 class="subsection" id="Next_002dmethod-1"><span>8.6.4 Next-method<a class="copiable-link" href="#Next_002dmethod-1"> ¶</a></span></h4>
|
|
|
|
<p>When you call a generic function, with a particular set of arguments,
|
|
GOOPS builds a list of all the methods that are applicable to those
|
|
arguments and orders them by how closely the method definitions match
|
|
the actual argument types. It then calls the method at the top of this
|
|
list. If the selected method’s code wants to call on to the next method
|
|
in this list, it can do so by using <code class="code">next-method</code>.
|
|
</p>
|
|
<div class="example lisp">
|
|
<pre class="lisp-preformatted">(define-method (Test (a <integer>)) (cons 'integer (next-method)))
|
|
(define-method (Test (a <number>)) (cons 'number (next-method)))
|
|
(define-method (Test a) (list 'top))
|
|
</pre></div>
|
|
|
|
<p>With these definitions,
|
|
</p>
|
|
<div class="example lisp">
|
|
<pre class="lisp-preformatted">(Test 1) ⇒ (integer number top)
|
|
(Test 1.0) ⇒ (number top)
|
|
(Test #t) ⇒ (top)
|
|
</pre></div>
|
|
|
|
<p><code class="code">next-method</code> is always called as just <code class="code">(next-method)</code>. The
|
|
arguments for the next method call are always implicit, and always the
|
|
same as for the original method call.
|
|
</p>
|
|
<p>If you want to call on to a method with the same name but with a
|
|
different set of arguments (as you might with overloaded methods in C++,
|
|
for example), you do not use <code class="code">next-method</code>, but instead simply
|
|
write the new call as usual:
|
|
</p>
|
|
<div class="example lisp">
|
|
<pre class="lisp-preformatted">(define-method (Test (a <number>) min max)
|
|
(if (and (>= a min) (<= a max))
|
|
(display "Number is in range\n"))
|
|
(Test a))
|
|
|
|
(Test 2 1 10)
|
|
-|
|
|
Number is in range
|
|
⇒
|
|
(integer number top)
|
|
</pre></div>
|
|
|
|
<p>(You should be careful in this case that the <code class="code">Test</code> calls do not
|
|
lead to an infinite recursion, but this consideration is just the same
|
|
as in Scheme code in general.)
|
|
</p>
|
|
</div>
|
|
<hr>
|
|
<div class="nav-panel">
|
|
<p>
|
|
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>
|
|
</div>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|