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copied!<p>Imagine you have the following generic function (all it does is pass arguments (called "forwarding") to the inner function <code>callme</code>):</p> <pre><code>template <typename T> void f(T& t) { callme(t); } </code></pre> <p>Now, pretend that the definition of <code>callme</code> looks like this: <code>void callme(const int& i)</code>. The problem is that <code>callme(1)</code> will work, but <code>f(1)</code> will not (this is because rvalues do not bind to non-const references). To solve this, you need to change <code>f</code> to: <code>f(const T& t)</code>. However, this introduces a new problem. If <code>callme</code> is defined like this: <code>void callme(int& i)</code>, you will get a compile error. The solution is to make two overloads for <code>f</code> to take both <code>f(const T& t)</code> and <code>f(T& t)</code>.</p> <p>Now, the above situation works fine when a function only takes a single argument. However, imagine a function that takes two arguments, you have to make 4 overloads:</p> <pre><code>f(const T1&, const T2&) f(const T1&, T2&) f(T1&, const T2&) f(T1&, T2&) </code></pre> <p><a href="http://blogs.msdn.com/b/vcblog/archive/2009/02/03/rvalue-references-c-0x-features-in-vc10-part-2.aspx" rel="nofollow">In this article on msdn</a>, it mentions that for <code>tr1::bind</code>, for 5 arguments, a total of 63 overloads was needed! What I have just explained is called the <a href="http://www.google.co.jp/search?q=forwarding+problem&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla%3aja%3aofficial&hl=ja&client=firefox-a" rel="nofollow">forwarding problem</a> which has been solved in <code>C++11</code> using perfect forwarding and rvalue references.</p> <p>Quote from Boost Site:</p> <p><code>The library chooses a small subset: for up to two arguments, it provides the const overloads in full, for arities of three and more it provides a single additional overload with all of the arguments taken by const reference.</code></p>

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