< cpp‎ | experimental‎ | ranges
Technical specifications
Filesystem library (filesystem TS)
Library fundamentals (library fundamentals TS)
Library fundamentals 2 (library fundamentals 2 TS)
Extensions for parallelism (parallelism TS)
Extensions for parallelism 2 (parallelism TS v2)
Extensions for concurrency (concurrency TS)
Concepts (concepts TS)
Ranges (ranges TS)
Special mathematical functions (special math TR)
General utilities library
Utility components
Function objects
Metaprogramming and type traits
Tagged pairs and tuples
template< class T = void >

    requires EqualityComparable<T> ||
             Same<T, void> ||
             /* == on two const T lvalues invokes a built-in operator comparing pointers */

struct not_equal_to;
(ranges TS)
template <>
struct not_equal_to<void>;
(ranges TS)

Function object for performing comparisons. The primary template invokes operator == on const lvalues of type T and negates the result. The specialization not_equal_to<void> deduces the parameter types of the function call operator from the arguments (but not the return type).

All specializations of not_equal_to are Semiregular.

Member types

Member type Definition
is_transparent (member only of not_equal_to<void> specialization) /* unspecified */

Member functions

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


constexpr bool operator()(const T& x, const T& y) const;
(1) (member only of primary not_equal_to<T> template)
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;
(2) (member only of not_equal_to<void> specialization)
1) Compares x and y. Equivalent to return !ranges::equal_to<>{}(x, y);
2) Compares t and u. Equivalent to return !ranges::equal_to<>{}(std::forward<T>(t), std::forward<U>(u));.


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


See also

function object implementing x != y
(class template)