Possible Duplicate:
how to provide a swap function for my class?
There are some questions about this, but a lot of contradictions (person A giving solution A' with many upvotes with person B saying it's UB) or "only works if the compiler supports ADL" is answered.
So, say I have the following template (container) class:
template<typename T>
class C {
// ...
void swap(C<T>& y) throw(); // C x; x.swap(y);
}
then what is the correct way to make sure this (example) code works:
C<int> x, y;
std::swap(x, y);
Please give your answer for C++03, and if it still works in C++0x, even better!
You are not allowed to overload functions in the std-namespace.
Declare swap as a free function, overloaded in the same namespace as your class C
:
template<class T>
void swap(C<T>& x, C<T>& y) { x.swap(y); }
The right way to swap is to import std::swap and use a non-qualified version (which is retreieved via namespace-based Koenig lookup):
template<class T>
void dostuff(T x, T y) {
...
using std::swap;
swap(x,y);
...
}
That will use C::swap if x and are C, and std::swap for types that do not have their own swap.
(The import of std::swap like above is only necessary in template functions where the type is not known. If you know you have a C, then you can use x.swap(y) right away w/o problems.)
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