std::ranges::less (3) - Linux Manuals

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


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


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 types

Member type Definition
is_transparent /* unspecified */

Member functions

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


template< class T, class U >
requires StrictTotallyOrderedWith<T, U> ||
/* std::declval<T>() < std::declval<U>() resolves to
a built-in operator comparing pointers */
constexpr bool operator()(T&& t, U&& u) const;

Compares t and u, equivalent to return std::forward<T>(t) < std::forward<U>(u);, except when that expression resolves to a call to a builtin operator< comparing pointers.
When a call would invoke a built-in operator comparing pointers of type P, the result is instead determined as follows:

* Returns true if the (possibly converted) value of the first argument precedes the (possibly converted) value of the second argument in the implementation-defined strict total ordering over all pointer values of type P. This strict total ordering is consistent with the partial order imposed by the builtin operators <, >, <=, and >=.
* Otherwise, returns false.

The behavior is undefined unless the the conversion sequences from both T and U to P are equality-preserving (see below).

Equality preservation

An expression is equality preserving if it results in equal outputs given equal inputs.

* The inputs to an expression consist of its operands.
* The outputs of an expression consist of its result and all operands modified by the expression (if any).

Every expression required to be equality preserving is further required to be stable: two evaluations of such an expression with the same input objects must have equal outputs absent any explicit intervening modification of those input objects.


Unlike std::less, std::ranges::less requires all six comparison operators <, <=, >, >=, == and != to be valid (via the StrictTotallyOrderedWith constraint).


 This section is incomplete
 Reason: no example

See also

     function object implementing x < y
less (class template)