NAME¶

std::ranges::less - std::ranges::less

Synopsis¶

Defined in header <functional>
struct less; (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 functions¶

operator() checks if the first argument is less than the second
(public member function)

std::ranges::less::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:

* If the converted t precedes the converted u (both are of type P) in the
implementation-defined strict total order over pointers, returns true, otherwise
returns false.
* 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::totally_ordered_with<T, U> is not modeled, the behavior is undefined.

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

If there exists an expression expr1 of type T and an expression expr2 of U, such
that the comparison results of expr1 and expr2 violate strict total ordering (rules
are defined below), the behavior is undefined.

The comparison results of expr1 and expr2 follow strict total ordering only if
exactly one of the following expressions is true:

* std::ranges::less{}(expr1, expr2)
* std::ranges::less{}(expr2, expr1)
* std::ranges::equal_to{}(expr1, expr2)

Notes¶

Unlike std::less, std::ranges::less requires all six comparison operators <, <=, >,
>=, == and != to be valid (via the totally_ordered_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¶

less function object implementing x < y
(class template)

Category:¶

* Todo no example