| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| <html> |
| <!-- Copyright (C) 1988-2015 Free Software Foundation, Inc. |
| |
| 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 the |
| Invariant Sections being "Funding Free Software", the Front-Cover |
| Texts being (a) (see below), and with the Back-Cover Texts being (b) |
| (see below). A copy of the license is included in the section entitled |
| "GNU Free Documentation License". |
| |
| (a) The FSF's Front-Cover Text is: |
| |
| A GNU Manual |
| |
| (b) The FSF's Back-Cover Text is: |
| |
| You have freedom to copy and modify this GNU Manual, like GNU |
| software. Copies published by the Free Software Foundation raise |
| funds for GNU development. --> |
| <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ --> |
| <head> |
| <title>Using the GNU Compiler Collection (GCC): Namespace Association</title> |
| |
| <meta name="description" content="Using the GNU Compiler Collection (GCC): Namespace Association"> |
| <meta name="keywords" content="Using the GNU Compiler Collection (GCC): Namespace Association"> |
| <meta name="resource-type" content="document"> |
| <meta name="distribution" content="global"> |
| <meta name="Generator" content="makeinfo"> |
| <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> |
| <link href="index.html#Top" rel="start" title="Top"> |
| <link href="Option-Index.html#Option-Index" rel="index" title="Option Index"> |
| <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> |
| <link href="C_002b_002b-Extensions.html#C_002b_002b-Extensions" rel="up" title="C++ Extensions"> |
| <link href="Type-Traits.html#Type-Traits" rel="next" title="Type Traits"> |
| <link href="Function-Multiversioning.html#Function-Multiversioning" rel="prev" title="Function Multiversioning"> |
| <style type="text/css"> |
| <!-- |
| a.summary-letter {text-decoration: none} |
| blockquote.smallquotation {font-size: smaller} |
| div.display {margin-left: 3.2em} |
| div.example {margin-left: 3.2em} |
| div.indentedblock {margin-left: 3.2em} |
| div.lisp {margin-left: 3.2em} |
| div.smalldisplay {margin-left: 3.2em} |
| div.smallexample {margin-left: 3.2em} |
| div.smallindentedblock {margin-left: 3.2em; font-size: smaller} |
| div.smalllisp {margin-left: 3.2em} |
| kbd {font-style:oblique} |
| pre.display {font-family: inherit} |
| pre.format {font-family: inherit} |
| pre.menu-comment {font-family: serif} |
| pre.menu-preformatted {font-family: serif} |
| pre.smalldisplay {font-family: inherit; font-size: smaller} |
| pre.smallexample {font-size: smaller} |
| pre.smallformat {font-family: inherit; font-size: smaller} |
| pre.smalllisp {font-size: smaller} |
| span.nocodebreak {white-space:nowrap} |
| span.nolinebreak {white-space:nowrap} |
| span.roman {font-family:serif; font-weight:normal} |
| span.sansserif {font-family:sans-serif; font-weight:normal} |
| ul.no-bullet {list-style: none} |
| --> |
| </style> |
| |
| |
| </head> |
| |
| <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> |
| <a name="Namespace-Association"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Type-Traits.html#Type-Traits" accesskey="n" rel="next">Type Traits</a>, Previous: <a href="Function-Multiversioning.html#Function-Multiversioning" accesskey="p" rel="prev">Function Multiversioning</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> |
| </div> |
| <hr> |
| <a name="Namespace-Association-1"></a> |
| <h3 class="section">7.9 Namespace Association</h3> |
| |
| <p><strong>Caution:</strong> The semantics of this extension are equivalent |
| to C++ 2011 inline namespaces. Users should use inline namespaces |
| instead as this extension will be removed in future versions of G++. |
| </p> |
| <p>A using-directive with <code>__attribute ((strong))</code> is stronger |
| than a normal using-directive in two ways: |
| </p> |
| <ul> |
| <li> Templates from the used namespace can be specialized and explicitly |
| instantiated as though they were members of the using namespace. |
| |
| </li><li> The using namespace is considered an associated namespace of all |
| templates in the used namespace for purposes of argument-dependent |
| name lookup. |
| </li></ul> |
| |
| <p>The used namespace must be nested within the using namespace so that |
| normal unqualified lookup works properly. |
| </p> |
| <p>This is useful for composing a namespace transparently from |
| implementation namespaces. For example: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">namespace std { |
| namespace debug { |
| template <class T> struct A { }; |
| } |
| using namespace debug __attribute ((__strong__)); |
| template <> struct A<int> { }; // <span class="roman">OK to specialize</span> |
| |
| template <class T> void f (A<T>); |
| } |
| |
| int main() |
| { |
| f (std::A<float>()); // <span class="roman">lookup finds</span> std::f |
| f (std::A<int>()); |
| } |
| </pre></div> |
| |
| |
| |
| |
| </body> |
| </html> |
