NAME

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

Synopsis

Defined in header <experimental/ranges/functional>
template< class T = void >

requires StrictTotallyOrdered<T> ||
Same<T, void> || (ranges TS)
/* < on two const T lvalues invokes a built-in operator comparing
pointers */

struct less;
template <> (ranges TS)
struct less<void>;

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& (1) (member only of primary less<T>
y) const; template)
template< class T, class U >

requires StrictTotallyOrderedWith<T, U> ||
/* std::declval<T>() < std::declval<U>() (2) (member only of less<void>
resolves to specialization)
a built-in operator comparing pointers */

constexpr bool operator()(T&& t, U&& u) const;

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).

Example