std::ranges::equal_to

 

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Operator wrappers plus minus negate multiplies divides modulus bit_and bit_or bit_not (C++14)   bit_xor equal_to not_equal_to greater less greater_equal less_equal logical_and logical_or logical_not	Transparent operator wrappers plus<> (C++14) minus<> (C++14) negate<> (C++14) multiplies<> (C++14)   divides<> (C++14) modulus<> (C++14) bit_and<> (C++14) bit_or<> (C++14) bit_not<> (C++14) bit_xor<> (C++14) equal_to<> (C++14) not_equal_to<> (C++14) greater<> (C++14) less<> (C++14) greater_equal<> (C++14) less_equal<> (C++14) logical_and<> (C++14) logical_or<> (C++14) logical_not<> (C++14)
Negators not_fn (C++17) Searchers default_searcher (C++17) boyer_moore_searcher (C++17) boyer_moore_horspool_searcher (C++17)	Constrained comparators ranges::equal_to (C++20) ranges::not_equal_to (C++20) ranges::greater (C++20) ranges::less (C++20) ranges::greater_equal (C++20) ranges::less_equal (C++20) compare_three_way (C++20)
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unary_function (until C++17*) binary_function (until C++17*) ptr_fun (until C++17*) pointer_to_unary_function (until C++17*) pointer_to_binary_function (until C++17*)   mem_fun (until C++17*) mem_fun_tmem_fun1_tconst_mem_fun_tconst_mem_fun1_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) not1 (until C++20*) not2 (until C++20*)	binder1stbinder2nd (until C++17*)(until C++17*) bind1stbind2nd (until C++17*)(until C++17*) mem_fun_ref (until C++17*) mem_fun_ref_tmem_fun1_ref_tconst_mem_fun_ref_tconst_mem_fun1_ref_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) unary_negate (until C++20*) binary_negate (until C++20*)

 

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.

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;

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).

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

equal_to

function object implementing x == y (class template)