cpp/experimental/ranges/iterator/difference type

Computes the associated difference type of the type, if any. Users may specialize for a program-defined type.

@1@ Primary template is an empty struct. @2@ Specialization for pointers. If is an object type, provides a member type  equal to std. Otherwise, there is no member. @3@ Specialization for const-qualified types. @4@ Specialization for types that define a public and accessible member type. Provides a member type equal to. @5@ Specialization for types that do not define a public and accessible member type but do support subtraction. Provides a member type equal to.