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    <p>While it's correct that one shouldn't generally add stuff to the std:: namespace, adding template specializations for user-defined types is specifically allowed. Overloading the functions is not. This is a subtle difference :-)</p> <blockquote> <p>17.4.3.1/1 It is undefined for a C++ program to add declarations or definitions to namespace std or namespaces with namespace std unless otherwise specified. A program may add template specializations for any standard library template to namespace std. Such a specialization (complete or partial) of a standard library results in undefined behaviour unless the declaration depends on a user-defined name of external linkage and unless the template specialization meets the standard library requirements for the original template. </p> </blockquote> <p>A specialization of std::swap would look like:</p> <pre><code>namespace std { template&lt;&gt; void swap(myspace::mytype&amp; a, myspace::mytype&amp; b) { ... } } </code></pre> <p>Without the template&lt;> bit it would be an overload, which is undefined, rather than a specialization, which is permitted. @Wilka's suggest approach of changing the default namespace may work with user code (due to Koenig lookup preferring the namespace-less version) but it's not guaranteed to, and in fact isn't really supposed to (the STL implementation ought to use the fully-qualified std::swap).</p> <p>There is a <a href="http://groups.google.ca/group/comp.lang.c++.moderated/browse_thread/thread/b396fedad7dcdc81" rel="noreferrer">thread on comp.lang.c++.moderated</a> with a <strong>long</strong> dicussion of the topic. Most of it is about partial specialization, though (which there's currently no good way to do).</p>
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    1. POHow to overload std::swap()
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    1. COOne reason it's wrong to use function template specialization for this (or anything): it interacts in bad ways with overloads, of which there are many for swap. For example, if you specialize the regular std::swap for std::vector<mytype>&, your specialization won't get chosen over the standard's vector-specific swap, because specializations aren't considered during overload resolution.
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    2. COThis is also what Meyers recommends in Effective C++ 3ed (Item 25, pp 106-112).
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