NAME¶

std::ranges::equal_to - std::ranges::equal_to

Synopsis¶

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

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

Member functions¶

operator() checks if the arguments are equal
(public member function)

std::ranges::equal_to::operator()

template< class T, class U >
constexpr bool operator()( T&& t, U&& u ) const;

Given the expression std::forward<T>(t) == std::forward<U>(u) as expr:

* If expr results in a call to built-in operator== comparing pointers, given the
composite pointer type of t and u as P:

* For the two converted pointers (of type P), if one pointer precedes the other in
the implementation-defined strict total order over pointers, returns false,
otherwise returns true.
* If the conversion sequence from T to P or the conversion sequence from U to P is
not equality-preserving, the behavior is undefined.
* Otherwise:

* Returns the result of expr.
* If std::equality_comparable_with<T, U> is not modeled, the behavior is
undefined.

This overload participates in overload resolution only if
std::equality_comparable_with<T, U> is satisfied.

Notes¶

Compared to std::equal_to, std::ranges::equal_to additionally requires != to be
valid, and that both argument types are required to be (homogeneously) comparable
with themselves (via the equality_comparable_with constraint).

Example¶

This section is incomplete
Reason: no example

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3530 C++20 syntactic checks were relaxed only semantic requirements are
while comparing pointers relaxed

See also¶

equal_to function object implementing x == y
(class template)

Category:¶

* Todo no example