std::incrementable_traits - cppreference.com
From cppreference.com
| Defined in header |
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template< class I > struct incrementable_traits {}; |
(1) | (since C++20) |
template< class T > requires std::is_object_v<T> struct incrementable_traits<T*>; |
(2) | (since C++20) |
template< class T > struct incrementable_traits<const T> : incrementable_traits<T> {}; |
(3) | (since C++20) |
template< class T > requires requires { typename T::difference_type; } struct incrementable_traits<T>; |
(4) | (since C++20) |
template< class T > requires (!requires { typename T::difference_type; }) && requires(const T& a, const T& b) { { a - b } -> std::integral; } struct incrementable_traits<T>; |
(5) | (since C++20) |
Computes the associated difference type of the type I, if any. A program may specialize incrementable_traits for a program-defined type.
1) Primary template is an empty struct.
2) Specialization for pointers.
Provides a member type difference_type same as std::ptrdiff_t.
3) Specialization for const-qualified types.
4) Specialization for types that define a public and accessible member type difference_type.
Provides a member type difference_type same as 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 difference_type same as std::make_signed_t<decltype(std::declval<T>() - std::declval<T>())>. The implicit expression variations rule (see below) applies to the expression a - b.
Implicit expression variations
A requires expression that uses an expression that is non-modifying for some constant lvalue operand also requires implicit expression variations.