Defined in header <compare> | ||
---|---|---|
class partial_ordering; | (since C++20) |
The class type std::partial_ordering
is the result type of a three-way comparison that.
The type std::partial_ordering
has four valid values, implemented as const static data members of its type:
Member constant | Definition |
---|---|
less(inline constexpr)
[static] | a valid value of the type std::partial_ordering indicating less-than (ordered before) relationship (public static member constant) |
equivalent(inline constexpr)
[static] | a valid value of the type std::partial_ordering indicating equivalence (neither ordered before nor ordered after) (public static member constant) |
greater(inline constexpr)
[static] | a valid value of the type std::partial_ordering indicating greater-than (ordered after) relationship (public static member constant) |
unordered(inline constexpr)
[static] | a valid value of the type std::partial_ordering indicating relationship with an incomparable value (public static member constant) |
std::partial_ordering
is implicitly-convertible to std::weak_equality
, while both std::strong_ordering
and std::weak_ordering
are implicitly-convertible to partial_ordering
.
operator weak_equality | implicit conversion to std::weak_equality (public member function) |
constexpr operator weak_equality() const noexcept; |
std::weak_equality::equivalent
if v
is equivalent
, std::weak_equality::nonequivalent
if v
is less
, greater
, or unordered
.
Comparison operators are defined between values of this type and literal 0
. This supports the expressions a <=> b == 0
or a <=> b < 0
that can be used to convert the result of a three-way comparison operator to a boolean relationship; see std::is_eq
, std::is_lt
, etc.
The behavior of a program that attempts to compare a partial_ordering
with anything other than the integer literal 0
is undefined.
operator==operator!=operator<operator>operator<=operator>=operator<=> | compares with zero (function) |
friend constexpr bool operator==(partial_ordering v, /*unspecified*/ u) noexcept; friend constexpr bool operator==(/*unspecified*/ u, partial_ordering v) noexcept; |
v | - | a std::partial_ordering value to check |
u | - | an unused parameter of any type that accepts literal zero argument |
true
if v
is equivalent
, false
if v
is less
, greater
, or unordered
.
friend constexpr bool operator!=(partial_ordering v, /*unspecified*/ u) noexcept; friend constexpr bool operator!=(/*unspecified*/ u, partial_ordering v) noexcept; |
v | - | a std::partial_ordering value to check |
u | - | an unused parameter of any type that accepts literal zero argument |
true
if v
is unordered
, less
, or greater
, and false
if v
is equivalent
.
friend constexpr bool operator<(partial_ordering v, /*unspecified*/ u) noexcept; | (1) | |
friend constexpr bool operator<(/*unspecified*/ u, partial_ordering v) noexcept; | (2) |
v | - | a std::partial_ordering value to check |
u | - | an unused parameter of any type that accepts literal zero argument |
true
if v
is less
, and false
if v
is greater
, equivalent
, or unordered
true
if v
is greater
, and false
if v
is less
, equivalent
, or unordered
friend constexpr bool operator<=(partial_ordering v, /*unspecified*/ u) noexcept; | (1) | |
friend constexpr bool operator<=(/*unspecified*/ u, partial_ordering v) noexcept; | (2) |
v | - | a std::partial_ordering value to check |
u | - | an unused parameter of any type that accepts literal zero argument |
true
if v
is less
or equivalent
, and false
if v
is greater
or unordered
true
if v
is greater
or equivalent
, and false
if v
is less
or unordered
friend constexpr bool operator>(partial_ordering v, /*unspecified*/ u) noexcept; | (1) | |
friend constexpr bool operator>(/*unspecified*/ u, partial_ordering v) noexcept; | (2) |
v | - | a std::partial_ordering value to check |
u | - | an unused parameter of any type that accepts literal zero argument |
true
if v
is greater
, and false
if v
is less
, equivalent
, or unordered
true
if v
is less
, and false
if v
is greater
, equivalent
, or unordered
friend constexpr bool operator>=(partial_ordering v, /*unspecified*/ u) noexcept; | (1) | |
friend constexpr bool operator>=(/*unspecified*/ u, partial_ordering v) noexcept; | (2) |
v | - | a std::partial_ordering value to check |
u | - | an unused parameter of any type that accepts literal zero argument |
true
if v
is greater
or equivalent
, and false
if v
is less
or unordered
true
if v
is less
or equivalent
, and false
if v
is greater
or unordered
friend constexpr partial_ordering operator<=>(partial_ordering v, /*unspecified*/ u) noexcept; | (1) | |
friend constexpr partial_ordering operator<=>(/*unspecified*/ u, partial_ordering v) noexcept; | (2) |
v | - | a std::partial_ordering value to check |
u | - | an unused parameter of any type that accepts literal zero argument |
v
.greater
if v
is less
, less
if v
is greater
, otherwise v
. The built-in operator <=> between floating-point values uses this ordering: the positive zero and the negative zero compare equivalent
, but can be distinguished, and NaN values compare unordered
with any other value.
(C++20) | the result type of 3-way comparison that supports all 6 operators and is substitutable (class) |
(C++20) | the result type of 3-way comparison that supports all 6 operators and is not substitutable (class) |
(C++20) | the result type of 3-way comparison that supports only equality/inequality and is substitutable (class) |
(C++20) | the result type of 3-way comparison that supports only equality/inequality and is not substitutable (class) |
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