forked from boostorg/mpl
83 lines
7.6 KiB
HTML
83 lines
7.6 KiB
HTML
<?xml version="1.0" encoding="utf-8" ?>
|
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
|
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
<meta name="generator" content="Docutils 0.3.6: http://docutils.sourceforge.net/" />
|
|
<title>The MPL Reference Manual: Metafunctions</title>
|
|
<link rel="stylesheet" href="../style.css" type="text/css" />
|
|
</head>
|
|
<body class="docframe refmanual">
|
|
<table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./reverse-stable-partition.html" class="navigation-link">Prev</a> <a href="./metafunctions-concepts.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./algorithms.html" class="navigation-link">Back</a> <a href="./data-types.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="../refmanual.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
|
|
<td class="header-group page-location"><a href="../refmanual.html" class="navigation-link">Front Page</a> / <a href="./metafunctions.html" class="navigation-link">Metafunctions</a></td>
|
|
</tr></table><div class="header-separator"></div>
|
|
<div class="section" id="metafunctions">
|
|
<h1><a class="toc-backref" href="../refmanual.html#id436" name="metafunctions">Metafunctions</a></h1>
|
|
<a class="target" id="label-metafunctions" name="label-metafunctions"></a><p>The MPL includes a number of predefined metafunctions that can be roughly
|
|
classified in two categories: <cite>general purpose metafunctions</cite>, dealing with
|
|
conditional <a class="reference" href="./type-selection.html">type selection</a> and higher-order metafunction <a class="reference" href="./invocation.html">invocation</a>,
|
|
<a class="reference" href="./composition-and-argument.html">composition</a>, and <a class="reference" href="./composition-and-argument.html">argument binding</a>, and <cite>numeric metafunctions</cite>,
|
|
incapsulating built-in and user-defined <a class="reference" href="./arithmetic-operations.html">arithmetic</a>, <a class="reference" href="./comparisons.html">comparison</a>,
|
|
<a class="reference" href="./logical-operations.html">logical</a>, and <a class="reference" href="./bitwise-operations.html">bitwise</a> operations.</p>
|
|
<p>Given that it is possible to perform integer numeric computations at
|
|
compile time using the conventional operators notation, the need for the
|
|
second category might be not obvious, but it in fact plays a cental role in
|
|
making programming with MPL seemingly effortless. In
|
|
particular, there are at least two contexts where built-in language
|
|
facilities fall short <a class="footnote-reference" href="#portability" id="id200" name="id200">[3]</a>:</p>
|
|
<ol class="arabic simple">
|
|
<li>Passing a computation to an algorithm.</li>
|
|
<li>Performing a computation on non-integer data.</li>
|
|
</ol>
|
|
<p>The second use case deserves special attention. In contrast to the built-in,
|
|
strictly integer compile-time arithmetics, the MPL numeric metafunctions are
|
|
<em>polymorphic</em>, with support for <em>mixed-type arithmetics</em>. This means that they
|
|
can operate on a variety of numeric types — for instance, rational,
|
|
fixed-point or complex numbers, — and that, in general, you are allowed to
|
|
freely intermix these types within a single expression. See <a class="reference" href="./numeric-metafunction.html">Numeric Metafunction</a> concept for more details on the MPL numeric infrastructure.</p>
|
|
<!-- The provided `infrastructure`__ allows easy plugging of user-defined numeric
|
|
types
|
|
Naturally, they also , meaning that you can perform a computation on the
|
|
arguments of different types, and the result will yeild the largest/most general
|
|
of them. For user-defined numeric types, they provide an `infrastructure`__ that
|
|
allows easy plugging and seemless integration with predefined library
|
|
types. details.
|
|
|
|
__ `Numeric Metafunction`_ -->
|
|
<p>To reduce a negative syntactical impact of the metafunctions notation
|
|
over the infix operator notation, all numeric metafunctions
|
|
allow to pass up to N arguments, where N is defined by the value of
|
|
<a class="refentry reference" href="./limit-metafunction-arity.html"><tt class="refentry literal"><span class="pre">BOOST_MPL_LIMIT_METAFUNCTION_ARITY</span></tt></a> configuration macro.</p>
|
|
<table class="footnote" frame="void" id="portability" rules="none">
|
|
<colgroup><col class="label" /><col /></colgroup>
|
|
<tbody valign="top">
|
|
<tr><td class="label"><a class="fn-backref" href="#id200" name="portability">[3]</a></td><td>All other considerations aside, as of the time of this writing
|
|
(early 2004), using built-in operators on integral constants still often
|
|
present a portability problem — many compilers cannot handle particular
|
|
forms of expressions, forcing us to use conditional compilation. Because MPL
|
|
numeric metafunctions work on types and encapsulate these kind of workarounds
|
|
internally, they elude these problems, so if you aim for portability, it is
|
|
generally adviced to use them in the place of the conventional operators, even
|
|
at the price of slightly decreased readability.</td></tr>
|
|
</tbody>
|
|
</table>
|
|
<!-- modtime: November 04, 2004 09:37:30 +0000 -->
|
|
<ul class="toc simple" id="outline">
|
|
<li><a class="reference" href="./metafunctions-concepts.html" id="id437" name="id437">Concepts</a></li>
|
|
<li><a class="reference" href="./type-selection.html" id="id445" name="id445">Type Selection</a></li>
|
|
<li><a class="reference" href="./invocation.html" id="id450" name="id450">Invocation</a></li>
|
|
<li><a class="reference" href="./composition-and-argument.html" id="id454" name="id454">Composition and Argument Binding</a></li>
|
|
<li><a class="reference" href="./arithmetic-operations.html" id="id461" name="id461">Arithmetic Operations</a></li>
|
|
<li><a class="reference" href="./comparisons.html" id="id468" name="id468">Comparisons</a></li>
|
|
<li><a class="reference" href="./logical-operations.html" id="id475" name="id475">Logical Operations</a></li>
|
|
<li><a class="reference" href="./bitwise-operations.html" id="id479" name="id479">Bitwise Operations</a></li>
|
|
<li><a class="reference" href="./trivial.html" id="id485" name="id485">Trivial</a></li>
|
|
<li><a class="reference" href="./miscellaneous.html" id="id487" name="id487">Miscellaneous</a></li>
|
|
</ul>
|
|
</div>
|
|
|
|
<div class="footer-separator"></div>
|
|
<table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./reverse-stable-partition.html" class="navigation-link">Prev</a> <a href="./metafunctions-concepts.html" class="navigation-link">Next</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./algorithms.html" class="navigation-link">Back</a> <a href="./data-types.html" class="navigation-link">Along</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="../refmanual.html" class="navigation-link">Up</a> <a href="../refmanual.html" class="navigation-link">Home</a></span><span class="navigation-group-separator"> | </span><span class="navigation-group"><a href="./refmanual_toc.html" class="navigation-link">Full TOC</a></span></td>
|
|
</tr></table></body>
|
|
</html>
|