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| 6 | <meta name="generator" content="Docutils 0.7: http://docutils.sourceforge.net/" /> | |
| 7 | <title>The MPL Reference Manual: Metafunctions</title> | |
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| 10 | <body class="docframe refmanual"> | |
| 11 | <table class="header"><tr class="header"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./for-each.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> | |
| 12 | <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> | |
| 13 | </tr></table><div class="header-separator"></div> | |
| 14 | <div class="section" id="metafunctions"> | |
| 15 | <h1><a class="toc-backref" href="../refmanual.html#id1510">Metafunctions</a></h1> | |
| 16 | <p id="label-metafunctions">The MPL includes a number of predefined metafunctions that can be roughly | |
| 17 | classified in two categories: <cite>general purpose metafunctions</cite>, dealing with | |
| 18 | conditional <a class="reference internal" href="./type-selection.html">type selection</a> and higher-order metafunction <a class="reference internal" href="./invocation.html">invocation</a>, | |
| 19 | <a class="reference internal" href="./composition-and-argument-binding.html">composition</a>, and <a class="reference internal" href="./composition-and-argument-binding.html">argument binding</a>, and <cite>numeric metafunctions</cite>, | |
| 20 | incapsulating built-in and user-defined <a class="reference internal" href="./arithmetic-operations.html">arithmetic</a>, <a class="reference internal" href="./comparisons.html">comparison</a>, | |
| 21 | <a class="reference internal" href="./logical-operations.html">logical</a>, and <a class="reference internal" href="./bitwise-operations.html">bitwise</a> operations.</p> | |
| 22 | <p>Given that it is possible to perform integer numeric computations at | |
| 23 | compile time using the conventional operators notation, the need for the | |
| 24 | second category might be not obvious, but it in fact plays a cental role in | |
| 25 | making programming with MPL seemingly effortless. In | |
| 26 | particular, there are at least two contexts where built-in language | |
| 27 | facilities fall short <a class="footnote-reference" href="#portability" id="id820">[3]</a>:</p> | |
| 28 | <ol class="arabic simple"> | |
| 29 | <li>Passing a computation to an algorithm.</li> | |
| 30 | <li>Performing a computation on non-integer data.</li> | |
| 31 | </ol> | |
| 32 | <p>The second use case deserves special attention. In contrast to the built-in, | |
| 33 | strictly integer compile-time arithmetics, the MPL numeric metafunctions are | |
| 34 | <em>polymorphic</em>, with support for <em>mixed-type arithmetics</em>. This means that they | |
| 35 | can operate on a variety of numeric types — for instance, rational, | |
| 36 | fixed-point or complex numbers, — and that, in general, you are allowed to | |
| 37 | freely intermix these types within a single expression. See <a class="reference internal" href="./numeric-metafunction.html">Numeric Metafunction</a> concept for more details on the MPL numeric infrastructure.</p> | |
| 38 | <!-- The provided `infrastructure`__ allows easy plugging of user-defined numeric | |
| 39 | types | |
| 40 | Naturally, they also , meaning that you can perform a computation on the | |
| 41 | arguments of different types, and the result will yeild the largest/most general | |
| 42 | of them. For user-defined numeric types, they provide an `infrastructure`__ that | |
| 43 | allows easy plugging and seemless integration with predefined library | |
| 44 | types. details. | |
| 45 | ||
| 46 | __ `Numeric Metafunction`_ --> | |
| 47 | <p>To reduce a negative syntactical impact of the metafunctions notation | |
| 48 | over the infix operator notation, all numeric metafunctions | |
| 49 | allow to pass up to N arguments, where N is defined by the value of | |
| 50 | <a class="reference internal" href="./limit-metafunction-arity.html">BOOST_MPL_LIMIT_METAFUNCTION_ARITY</a> configuration macro.</p> | |
| 51 | <table class="docutils footnote" frame="void" id="portability" rules="none"> | |
| 52 | <colgroup><col class="label" /><col /></colgroup> | |
| 53 | <tbody valign="top"> | |
| 54 | <tr><td class="label"><a class="fn-backref" href="#id820">[3]</a></td><td>All other considerations aside, as of the time of this writing | |
| 55 | (early 2004), using built-in operators on integral constants still often | |
| 56 | present a portability problem — many compilers cannot handle particular | |
| 57 | forms of expressions, forcing us to use conditional compilation. Because MPL | |
| 58 | numeric metafunctions work on types and encapsulate these kind of workarounds | |
| 59 | internally, they elude these problems, so if you aim for portability, it is | |
| 60 | generally adviced to use them in the place of the conventional operators, even | |
| 61 | at the price of slightly decreased readability.</td></tr> | |
| 62 | </tbody> | |
| 63 | </table> | |
| 64 | <ul class="toc simple" id="outline"> | |
| 65 | <li><a class="reference internal" href="./metafunctions-concepts.html" id="id1511">Concepts</a></li> | |
| 66 | <li><a class="reference internal" href="./type-selection.html" id="id1519">Type Selection</a></li> | |
| 67 | <li><a class="reference internal" href="./invocation.html" id="id1524">Invocation</a></li> | |
| 68 | <li><a class="reference internal" href="./composition-and-argument-binding.html" id="id1528">Composition and Argument Binding</a></li> | |
| 69 | <li><a class="reference internal" href="./arithmetic-operations.html" id="id1535">Arithmetic Operations</a></li> | |
| 70 | <li><a class="reference internal" href="./comparisons.html" id="id1542">Comparisons</a></li> | |
| 71 | <li><a class="reference internal" href="./logical-operations.html" id="id1549">Logical Operations</a></li> | |
| 72 | <li><a class="reference internal" href="./bitwise-operations.html" id="id1553">Bitwise Operations</a></li> | |
| 73 | <li><a class="reference internal" href="./trivial.html" id="id1559">Trivial</a></li> | |
| 74 | <li><a class="reference internal" href="./string-operations.html" id="id1561">String Operations</a></li> | |
| 75 | <li><a class="reference internal" href="./miscellaneous.html" id="id1563">Miscellaneous</a></li> | |
| 76 | </ul> | |
| 77 | </div> | |
| 78 | ||
| 79 | <div class="footer-separator"></div> | |
| 80 | <table class="footer"><tr class="footer"><td class="header-group navigation-bar"><span class="navigation-group"><a href="./for-each.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> | |
| 81 | <td><div class="copyright-footer"><div class="copyright">Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams</div> | |
| 82 | Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 83 | file LICENSE_1_0.txt or copy at <a class="reference external" href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)</div></td></tr></table></body> | |
| 84 | </html> |