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132 lines
5.1 KiB
HTML
132 lines
5.1 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
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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 the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>C++ Concepts (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="C++ Concepts (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="C++ Concepts (Using the GNU Compiler Collection (GCC))">
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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="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="C_002b_002b-Extensions.html#C_002b_002b-Extensions" rel="up" title="C++ Extensions">
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<link href="Deprecated-Features.html#Deprecated-Features" rel="next" title="Deprecated Features">
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<link href="Type-Traits.html#Type-Traits" rel="prev" title="Type Traits">
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<style type="text/css">
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</style>
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</head>
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<body lang="en">
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<a name="C_002b_002b-Concepts"></a>
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<div class="header">
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<p>
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Next: <a href="Deprecated-Features.html#Deprecated-Features" accesskey="n" rel="next">Deprecated Features</a>, Previous: <a href="Type-Traits.html#Type-Traits" accesskey="p" rel="prev">Type Traits</a>, Up: <a href="C_002b_002b-Extensions.html#C_002b_002b-Extensions" accesskey="u" rel="up">C++ Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="C_002b_002b-Concepts-1"></a>
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<h3 class="section">7.10 C++ Concepts</h3>
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<p>C++ concepts provide much-improved support for generic programming. In
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particular, they allow the specification of constraints on template arguments.
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The constraints are used to extend the usual overloading and partial
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specialization capabilities of the language, allowing generic data structures
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and algorithms to be “refined” based on their properties rather than their
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type names.
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</p>
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<p>The following keywords are reserved for concepts.
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</p>
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<dl compact="compact">
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<dt><code>assumes</code></dt>
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<dd><p>States an expression as an assumption, and if possible, verifies that the
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assumption is valid. For example, <code>assume(n > 0)</code>.
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</p>
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</dd>
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<dt><code>axiom</code></dt>
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<dd><p>Introduces an axiom definition. Axioms introduce requirements on values.
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</p>
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</dd>
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<dt><code>forall</code></dt>
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<dd><p>Introduces a universally quantified object in an axiom. For example,
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<code>forall (int n) n + 0 == n</code>).
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</p>
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</dd>
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<dt><code>concept</code></dt>
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<dd><p>Introduces a concept definition. Concepts are sets of syntactic and semantic
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requirements on types and their values.
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</p>
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</dd>
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<dt><code>requires</code></dt>
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<dd><p>Introduces constraints on template arguments or requirements for a member
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function of a class template.
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</p>
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</dd>
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</dl>
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<p>The front end also exposes a number of internal mechanism that can be used
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to simplify the writing of type traits. Note that some of these traits are
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likely to be removed in the future.
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</p>
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<dl compact="compact">
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<dt><code>__is_same (type1, type2)</code></dt>
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<dd><p>A binary type trait: true whenever the type arguments are the same.
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</p>
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</dd>
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</dl>
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</body>
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</html>
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