std::experimental::ranges::difference_type

 

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Defined in header <experimental/ranges/iterator>
template< class I > struct difference_type { };	(1)
template< class T > struct difference_type<T*>;	(2)
template< class T > struct difference_type<const T> : difference_type<std::decay_t<T>> { };	(3)
template <class T>   requires requires { typename T::difference_type; } struct difference_type<T>;	(4)
template <class T>   requires !requires { typename T::difference_type; } &&            requires(const T& a, const T& b) { { a - b } -> Integral; } struct difference_type<T>;	(5)

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

1) Primary template is an empty struct.

2) Specialization for pointers. If T is an object type, provides a member type type equal to std::ptrdiff_t. Otherwise, there is no member type.

3) Specialization for const-qualified types.

4) Specialization for types that define a public and accessible member type difference_type. Provides a member type type equal to T::difference_type.

5) Specialization for types that do not define a public and accessible member type difference_type but do support subtraction. Provides a member type type equal to std::make_signed_t<decltype(std::declval<T>() - std::declval<T>())>.

Helper alias template

template< class T > using difference_type_t = typename ranges::difference_type<T>::type;		(ranges TS)

See also

WeaklyIncrementable	specifies that a Semiregular type can be incremented with pre- and post-increment operators (concept)
iterator_traits	compatibility traits class that collects an iterator’s associated types (alias template)