std::partial_order
Defined in header <compare> |
||
---|---|---|
inline namespace /* unspecified */ { inline constexpr /* unspecified */ partial_order = /* unspecified */; } |
(since C++20) | |
Call signature | ||
template< class T, class U > requires /* see below */ constexpr std::partial_ordering partial_order(T&& t, U&& u) noexcept(/* see below */); |
Compares two values using 3-way comparison and produces a result of type std::partial_ordering
.
Let t
and u
be expressions and T
and U
denote decltype((t))
and decltype((u))
respectively, std::partial_order(t, u)
is expression-equivalent to:
- If
std::is_same_v<std::decay_t<T>, std::decay_t<U>>
istrue
:-
std::partial_ordering(partial_order(t, u))
, if it is a well-formed expression with overload resolution performed in a context that does not include a declaration ofstd::partial_order
, - otherwise,
std::partial_ordering(std::compare_three_way()(t, u))
, if it is well-formed, - otherwise,
std::partial_ordering(std::weak_order(t, u))
, if it is well-formed,
-
- In all other cases, the expression is ill-formed, which can result in substitution failure when it appears in the immediate context of a template instantiation.
Expression-equivalent
Expression e
is expression-equivalent to expression f
, if.
-
e
andf
have the same effects, and - either both are constant subexpressions or else neither is a constant subexpression, and
- either both are potentially-throwing or else neither is potentially-throwing (i.e.
noexcept(e) == noexcept(f)
).
Customization point objects
The name std::partial_order
denotes a customization point object, which is a const function object of a literal semiregular
class type. For exposition purposes, the cv-unqualified version of its type is denoted as __partial_order_fn
.
All instances of __partial_order_fn
are equal. The effects of invoking different instances of type __partial_order_fn
on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). Thus, std::partial_order
can be copied freely and its copies can be used interchangeably.
Given a set of types Args...
, if std::declval<Args>()...
meet the requirements for arguments to std::partial_order
above, __partial_order_fn
models
.
-
std::invocable<__partial_order_fn, Args...>
, -
std::invocable<const __partial_order_fn, Args...>
, -
std::invocable<__partial_order_fn&, Args...>
, and -
std::invocable<const __partial_order_fn&, Args...>
.
Otherwise, no function call operator of __partial_order_fn
participates in overload resolution.
Notes
Example
See also
(C++20)
|
the result type of 3-way comparison that supports all 6 operators, is not substitutable, and allows incomparable values (class) |
(C++20)
|
performs 3-way comparison and produces a result of type std::strong_ordering (customization point object) |
(C++20)
|
performs 3-way comparison and produces a result of type std::weak_ordering (customization point object) |
(C++20)
|
performs 3-way comparison and produces a result of type std::partial_ordering , even if operator<=> is unavailable (customization point object) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/utility/compare/partial_order