More C++ Idioms/Enable if

Intent
Sometimes a member function of a class template (possibly one of an overloaded set) only makes sense for certain template parameters. The enable_if idiom uses SFINAE to eliminate unwanted functions before overload resolution.

Known Uses
One use of enable_if is in implementing requirements such as that on the (size_type, value_type) constructor of a standard container, which has special behavior if the value_type is an integral type. More primitive solutions exist, but enable_if is elegant in this context.

Related Idioms
SFINAE, metafunctions.