std::ranges::equal_to
From cppreference.com
< cpp | utility | functional
| Defined in header <functional>
|
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| 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.
Nested types
| Nested type | Definition |
is_transparent
|
unspecified |
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; |
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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
TtoPor the conversion sequence fromUtoPis not equality-preserving, the behavior is undefined.
- For the two converted pointers (of type
- 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 while comparing pointers | only semantic requirements are relaxed |
See also
| function object implementing x == y (class template) |