std::experimental::ranges::less

 

C++

Compiler support

Freestanding and hosted

Language

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Technical specifications

Filesystem library (filesystem TS)

Library fundamentals (library fundamentals TS)

Library fundamentals 2 (library fundamentals TS v2)

Library fundamentals 3 (library fundamentals TS v3)

Extensions for parallelism (parallelism TS)

Extensions for parallelism 2 (parallelism TS v2)

Extensions for concurrency (concurrency TS)

Extensions for concurrency 2 (concurrency TS v2)

Concepts (concepts TS)

Ranges (ranges TS)

Reflection (reflection TS)

Mathematical special functions (special functions TR)

 

Ranges

Concepts

General utilities

Iterators

Ranges

Algorithms

 

General utilities library

Utility components
swap	exchange
Function objects
invoke identity	equal_to not_equal_to	greater less	greater_equal less_equal
Metaprogramming and type traits
is_swappable_withis_swappable	is_nothrow_swappable_withis_nothrow_swappable	common_reference common_type
Tagged pairs and tuples
TagSpecifier TaggedType	tagged tag specifiers	tagged_pair make_tagged_pair	tagged_tuple make_tagged_tuple

 

Defined in header <experimental/ranges/functional>
template< class T = void >     requires StrictTotallyOrdered<T> ||              Same<T, void> ||              /* < on two const T lvalues invokes a built-in operator comparing pointers */ struct less;		(ranges TS)
template <> struct less<void>;		(ranges TS)

Function object for performing comparisons. The primary template invokes operator< on const lvalues of type T. The specialization less<void> deduces the parameter types of the function call operator from the arguments (but not the return type).

All specializations of less are Semiregular.

Member types

Member type	Definition
is_transparent (member only of less<void> specialization)	/* unspecified */

Member functions

operator()

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

std::experimental::ranges::less::operator()

constexpr bool operator()(const T& x, const T& y) const;	(1)	(member only of primary less<T> template)
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;	(2)	(member only of less<void> specialization)

1) Compares x and y. Equivalent to return ranges::less<>{}(x, y);

2) 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 to (1) or (2) 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 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.

Notes

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

See also

less	function object implementing x < y (class template)