How Can I Provide a Custom Swap Function for Use with STL Algorithms?

Providing a Swap Function for STL Algorithms

To enable the use of a custom swap method in STL algorithms, there are several approaches:

1. Member Swap:

   • This involves defining a member swap function within the class that implements the desired swap behavior.

2. Free-Standing Swap Function:

   • Define a separate swap function with the same namespace as the class. This function must be named swap and take the same arguments as the desired swap behaviour.

3. Explicit Specialization of std::swap:

   • While partial specialization of std::swap is not possible, explicit specialization can be used, but it is generally not recommended for function templates.

Recommended Approach:

The recommended approach is to use a free-standing swap function in the same namespace as the class. This allows the use of ADL (Argument-Dependent Lookup) when calling swap within STL algorithms.

Example:

namespace Foo {

class Bar{}; // dummy

void swap(Bar& lhs, Bar& rhs) {
    // ...
}

}

Using the above swap function within an STL algorithm:

template<class T>
void foo(T&amp; lhs, T&amp; rhs) {
    using std::swap; // enable 'std::swap' to be found
                    // if no other 'swap' is found through ADL
    // some code ...
    swap(lhs, rhs); // unqualified call, uses ADL and finds a fitting 'swap'
                    // or falls back on 'std::swap'
    // more code ...
}

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