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<h3><a href="../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../boost.png" border="0"></a></h3>
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<h1 align="center">Serialization</h1>
<h2 align="center"><code style="white-space: normal">BOOST_STRONG_TYPEDEF</code></h2>
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<hr>
<h3>Motivation</h3>
<code style="white-space: normal">typedef</code> creates an alias for an existing type. It does not create
a new type that can be used for matching either function or template parameters.
This can be shown by trying to compile the following example.
<pre></code>
typedef int a;
void f(int x); // (1) function to handle simple integers
void f(a x); // (2) special function to handle integers of type a
int main(){
int x = 1;
a y;
y = x; // other operations permitted as a is converted as necessary
f(x); // chooses (1)
f(y); // chooses (2)
}
</code></pre>
Since typedef doesn't create a new type, this program can't compile to code
that implements its obvious intention.
<p>
Usage of BOOST_STRONG_TYPEDEF
addresses this.
<pre></code>
<a target="strong_typedef" href="../../../boost/strong_typedef.hpp">
#include <boost/strong_typedef.hpp>
</a>
BOOST_STRONG_TYPEDEF(int, a)
void f(int x); // (1) function to handle simple integers
void f(a x); // (2) special function to handle integers of type a
int main(){
int x = 1;
a y;
y = x; // other operations permitted as a is converted as necessary
f(x); // chooses (1)
f(y); // chooses (2)
}
</code></pre>
The program will now compile and run as expected.
<h3>Usage</h3>
Syntax of <code style="white-space: normal">BOOST_STRONG_TYPEDEF</code>
has been designed to be similar to the standard
<code style="white-space: normal">typedef</code>. So
<pre><code>
BOOST_STRONG_TYPEDEF(primitive type, name)
</code></pre>
will create a new type "name" which will be substitutable for the original
type but still of distinct type.
<h3>Implemenation</h3>
<code style="white-space: normal">BOOST_STRONG_TYPEDEF</code> is a macro
which generates a class named "name" wraps and instance of its
primitive type and provides appropriate conversion operators in order
to make the new type substitutable for the one that it wraps.
<hr>
<p><i>© Copyright <a href="http://www.rrsd.com">Robert Ramey</a> 2002-2004.
Distributed under the Boost Software License, Version 1.0. (See
accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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