Function Overloading vs. Template Specialization for `std::swap`: Which Approach Should You Choose?

Template Specialization vs Function Overloading for Function Templates

When extending standard library functions like swap, you can choose between template specialization or function overloading. This raises the following questions:

1. Which Approach is Better?

The preferred method is function overloading.

2. Why is Function Overloading Better?

C prioritizes overload resolution over specialization. In the case of overloads and specializations with identical parameters (such as swap(Foo&, Foo&) specialized to swap), the overload will always be called.

Specialization Limitations with Standard Library Functions

When specializing standard library functions in the std namespace, there are limitations:

• Partial function specialization is not supported: This prevents specializing functions like swap with template parameters.
• Overloading is technically prohibited: The C standard prohibits adding overloads to the std namespace.

Workarounds for std::swap Specialization

Despite the limitations, there are two options for specializing std::swap for template classes:

1. Create an overload in a separate namespace (e.g., ::swap(Foo&, Foo&)) and rely on ADL for name lookup. However, this may not work if the standard library uses std::swap directly.
2. Ignore the restriction against overloads in the std namespace and add them directly. While technically not allowed, it often works in practice.

Remember that the standard library may not always use std::swap. Some algorithms use std::iter_swap, which may have its own implementation.

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