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<HTML><!-- -- Copyright (c) 1996-1999 -- Silicon Graphics Computer Systems, Inc. -- -- Permission to use, copy, modify, distribute and sell this software -- and its documentation for any purpose is hereby granted without fee, -- provided that the above copyright notice appears in all copies and -- that both that copyright notice and this permission notice appear -- in supporting documentation. Silicon Graphics makes no -- representations about the suitability of this software for any -- purpose. It is provided "as is" without express or implied warranty. -- -- Copyright (c) 1994 -- Hewlett-Packard Company -- -- Permission to use, copy, modify, distribute and sell this software -- and its documentation for any purpose is hereby granted without fee, -- provided that the above copyright notice appears in all copies and -- that both that copyright notice and this permission notice appear -- in supporting documentation. Hewlett-Packard Company makes no -- representations about the suitability of this software for any -- purpose. It is provided "as is" without express or implied warranty. -- --><Head><Title>identity<T></Title><!-- Generated by htmldoc --></HEAD><BODY BGCOLOR="#ffffff" LINK="#0000ee" TEXT="#000000" VLINK="#551a8b" ALINK="#ff0000"> <IMG SRC="CorpID.gif" ALT="SGI" HEIGHT="43" WIDTH="151"> <!--end header--><BR Clear><H1>identity<T></H1><Table CellPadding=0 CellSpacing=0 width=100%><TR><TD Align=left><Img src = "functors.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right><Img src = "type.gif" Alt="" WIDTH = "194" HEIGHT = "39" ></TD></TR><TR><TD Align=left VAlign=top><b>Category</b>: functors</TD><TD Align=right VAlign=top><b>Component type</b>: type</TD></TR></Table><h3>Description</h3><tt>Identity</tt> is a <A href="UnaryFunction.html">Unary Function</A> that represents the identityfunction: it takes a single argument <tt>x</tt>, and returns <tt>x</tt>.<h3>Example</h3><pre>int main(){ int x = 137; identity<int> id; assert(x == id(x)); } </pre><h3>Definition</h3>Defined in the standard header <A href="functional">functional</A>, and in the nonstandardbackward-compatibility header <A href="function.h">function.h</A>. This class is an SGIextension; it is not part of the C++ standard.<h3>Template parameters</h3><Table border><TR><TH>Parameter</TH><TH>Description</TH><TH>Default</TH></TR><TR><TD VAlign=top><tt>T</tt></TD><TD VAlign=top>The function object's argument type, and return type. <A href="#1">[1]</A></TD><TD VAlign=top> </TD></tr></table><h3>Model of</h3><A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A><h3>Type requirements</h3>None.<h3>Public base classes</h3><tt><A href="unary_function.html">unary_function</A><T, T></tt><h3>Members</h3><Table border><TR><TH>Member</TH><TH>Where defined</TH><TH>Description</TH></TR><TR><TD VAlign=top><tt>argument_type</tt></TD><TD VAlign=top> <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A></TD><TD VAlign=top>The type of <tt>identity</tt>'s argument: <tt>T</tt>.</TD></TR><TR><TD VAlign=top><tt>result_type</tt></TD><TD VAlign=top> <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A></TD><TD VAlign=top>The type of the result: <tt>T</tt>. <A href="#1">[1]</A></TD></TR><TR><TD VAlign=top><tt>const T& operator()(const T&) const</tt></TD><TD VAlign=top> <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A></TD><TD VAlign=top>Function call. The return value is simply the argument.</TD></tr></table><h3>New members</h3>All of <tt>identity</tt>'s members are defined in the <A href="AdaptableUnaryFunction.html">Adaptable Unary Function</A>requirements. <tt>Identity</tt> does not introduce any new members.<h3>Notes</h3><P><A name="1">[1]</A>It is essential that the return type and the argument type arethe same: generalizing <tt>identity</tt> to allow them to differ would notwork. The reason is that <tt>identity</tt> returns a const reference toits argument, rather than a copy of its argument. If <tt>identity</tt> wereallowed to perform a conversion, then this would be a dangling reference.<h3>See also</h3>The <A href="functors.html">function object overview</A>, <tt><A href="select1st.html">select1st</A></tt>, <tt><A href="select2nd.html">select2nd</A></tt>, <tt><A href="project1st.html">project1st</A></tt>, <tt><A href="project2nd.html">project2nd</A></tt><!--start footer--> <HR SIZE="6"><A href="http://www.sgi.com/"><IMG SRC="surf.gif" HEIGHT="54" WIDTH="54" ALT="[Silicon Surf]"></A><A HREF="index.html"><IMG SRC="stl_home.gif" HEIGHT="54" WIDTH="54" ALT="[STL Home]"></A><BR><FONT SIZE="-2"><A href="http://www.sgi.com/Misc/sgi_info.html" TARGET="_top">Copyright © 1999 Silicon Graphics, Inc.</A> All Rights Reserved.</FONT><FONT SIZE="-3"><a href="http://www.sgi.com/Misc/external.list.html" TARGET="_top">TrademarkInformation</A></FONT><P></BODY></HTML> ⌨️ 快捷键说明
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