libstdc++-v3/doc/html/manual/ext_compile_checks.html

   1 <?xml version="1.0" encoding="UTF-8" standalone="no"?>
   2 <!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"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 16. Compile Time Checks</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.78.1" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="extensions.html" title="Part III.  Extensions" /><link rel="prev" href="ext_preface.html" title="" /><link rel="next" href="debug_mode.html" title="Chapter 17. Debug Mode" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 16. Compile Time Checks</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ext_preface.html">Prev</a> </td><th width="60%" align="center">Part III.
   3   Extensions
   4
   5 </th><td width="20%" align="right"> <a accesskey="n" href="debug_mode.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.compile_checks"></a>Chapter 16. Compile Time Checks</h2></div></div></div><p>
   6     Also known as concept checking.
   7   </p><p>In 1999, SGI added <span class="emphasis"><em>concept checkers</em></span> to their implementation
   8       of the STL:  code which checked the template parameters of
   9       instantiated pieces of the STL, in order to insure that the parameters
  10       being used met the requirements of the standard.  For example,
  11       the Standard requires that types passed as template parameters to
  12       <code class="code">vector</code> be <span class="quote">“<span class="quote">Assignable</span>”</span> (which means what you think
  13       it means).  The checking was done during compilation, and none of
  14       the code was executed at runtime.
  15    </p><p>Unfortunately, the size of the compiler files grew significantly
  16       as a result.  The checking code itself was cumbersome.  And bugs
  17       were found in it on more than one occasion.
  18    </p><p>The primary author of the checking code, Jeremy Siek, had already
  19       started work on a replacement implementation.  The new code has been
  20       formally reviewed and accepted into
  21       <a class="link" href="http://www.boost.org/libs/concept_check/concept_check.htm" target="_top">the
  22       Boost libraries</a>, and we are pleased to incorporate it into the
  23       GNU C++ library.
  24    </p><p>The new version imposes a much smaller space overhead on the generated
  25       object file.  The checks are also cleaner and easier to read and
  26       understand.
  27    </p><p>They are off by default for all versions of GCC from 3.0 to 3.4 (the
  28       latest release at the time of writing).
  29       They can be enabled at configure time with
  30       <a class="link" href="configure.html" title="Configure"><code class="literal">--enable-concept-checks</code></a>.
  31       You can enable them on a per-translation-unit basis with
  32       <code class="code">#define _GLIBCXX_CONCEPT_CHECKS</code> for GCC 3.4 and higher
  33       (or with <code class="code">#define _GLIBCPP_CONCEPT_CHECKS</code> for versions
  34       3.1, 3.2 and 3.3).
  35    </p><p>Please note that the upcoming C++ standard has first-class
  36    support for template parameter constraints based on concepts in the core
  37    language. This will obviate the need for the library-simulated concept
  38    checking described above.
  39    </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ext_preface.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="extensions.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="debug_mode.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"> </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 17. Debug Mode</td></tr></table></div></body></html>