<!doctype html public "-//ietf//dtd html//en">
<html><head><title>boost::mpl::replace_if</title>
<link rel="stylesheet" href="../mpl_wiki.css">
</head><body bgcolor="white">
<h1><a href="../Table_of_Contents.html"><img src="../mpl_logo.jpg" alt="[Home]" border=0 align="right"></a>replace_if</h1><h3>Synopsis</h3>
<p>
<pre>
template<
typename Sequence
, typename Pred
, typename NewType
>
struct replace_if
{
typedef <em>unspecified</em> type;
};
</pre>
<p>
<h3>Description</h3>
<p>
Performs a conditional replacement operation on the sequence. The algorithm returns a new sequence which contains all the elements from <code>[begin<Sequence>::type, end<Sequence>::type)</code> range where every type that satisfies the predicate <code>Pred</code> has been replaced with a <code>NewType</code>. The result sequence preserves all the functional and performance characteristics of the original <code>Sequence</code>, including its size, but not identity.
<p>
<h3>Definition</h3>
<p>
<pre>
#include "<a href="../../../../../boost/mpl/replace_if.hpp">boost/mpl/replace_if.hpp</a>"
</pre>
<p>
<h3>Parameters</h3>
<table border="1">
<tr><th> Parameter </th><th> Requirement </th><th> Description </th></tr>
<tr><td><code>Sequence</code></td><td>A model of <a href="../Extensible_Sequence.html">Extensible Sequence</a></td><td>The original sequence. </td></tr>
<tr><td><code>Pred</code></td><td>An unary Predicate [Lambda Expression]</td><td>The replacement condition. </td></tr>
<tr><td><code>NewType</code></td><td>A type</td><td>A type to replace with. </td></tr>
</table>
<p>
<h3>Expression semantics</h3>
<p>
<table border="1">
<tr><th> Expression </th><th> Expression type </th><th> Precondition </th><th> Semantics </th><th> Postcondition </th></tr>
<tr><td><code>typedef replace_if<Sequence,Pred,NewType>::type s;</code></td><td>A model of <a href="../Extensible_Sequence.html">Extensible Sequence</a></td><td></td><td>Equivalent to <code>typedef lambda<Pred>::type pred; typedef transform< Sequence, if_< apply1<pred,_1>,NewType,_1> >::type t;</code>.</td><td></td></tr>
</table>
<p>
<h3>Complexity</h3>
<p>
Linear. Performs exactly <code><a href="../Reference/size.html">size</a><Sequence>::type::value</code> applications of <code>Pred</code>, and at most <code><a href="../Reference/size.html">size</a><Sequence>::type::value</code> insertions.
<p>
<h3>Example</h3>
<p>
<pre>
typedef <a href="../Reference/list_c.html">list_c</a><int,1,4,5,2,7,5,3,5>::type numbers;
typedef replace_if< numbers, greater<_,4>, int_<0> >::type result;
typedef <a href="../Reference/list_c.html">list_c</a><int,1,4,0,2,0,0,3,0>::type answer;
BOOST_STATIC_ASSERT((<a href="../Reference/equal.html">equal</a>< answer,result >::type::value));
</pre>
<p>
<h3>See also</h3>
<p>
<a href="../Algorithms.html">Algorithms</a>, <code><a href="../Reference/replace.html">replace</a></code>, <code><a href="../Reference/transform.html">transform</a></code>
<p><hr>
<a href="../Table_of_Contents.html">Table of Contents</a><br>Last edited March 12, 2003 6:32 am</body></html>
