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std::ranges::not_equal_to

Defined in header `<functional>`
struct not_equal_to;		(since C++20)

Function object for performing comparisons. Deduces the parameter types of the function call operator from the arguments (but not the return type).

Member types

Member type	Definition
`is_transparent`	/* unspecified */

Member functions

operator()

checks if the arguments are not equal
(public member function)

std::ranges::not_equal_to::operator()

template< class T, class U >
    requires EqualityComparableWith<T, U> ||
             /* std::declval<T>() == std::declval<U>() resolves to
                a built-in operator comparing pointers */
constexpr bool operator()(T&& t, U&& u) const;

Compares t and u. Equivalent to return !ranges::equal_to{}(std::forward<T>(t), std::forward<U>(u));.

Notes

Unlike std::not_equal_to, std::ranges::not_equal_to requires both == and != to be valid (via the EqualityComparableWith constraint), and is entirely defined in terms of std::ranges::equal_to. However, the implementation is free to use operator!= directly, because those concepts require the results of == and != to be consistent.