std::strong_ordering
Defined in header <compare> |
||
---|---|---|
class strong_ordering; |
(since C++20) |
The class type std::strong_ordering
is the result type of a three-way comparison that.
- admits all six relational operators (==, !=, <, <=, >, >=)
- implies substitutability: if a is equivalent to b, f(a) is also equivalent to f(b), where f denotes a function that reads only comparison-salient state that is accessible via the argument's public const members. In other words, equivalent values are indistinguishable.
- does not allow incomparable values: exactly one of a < b, a == b, or a > b must be true
Constants
The type std::strong_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::strong_ordering indicating less-than (ordered before) relationship (public static member constant) |
equivalent(inline constexpr)
[static]
|
a valid value of the type std::strong_ordering indicating equivalence (neither ordered before nor ordered after), the same as equal (public static member constant) |
equal(inline constexpr)
[static]
|
a valid value of the type std::strong_ordering indicating equivalence (neither ordered before nor ordered after), the same as equivalent (public static member constant) |
greater(inline constexpr)
[static]
|
a valid value of the type std::strong_ordering indicating greater-than (ordered after) relationship (public static member constant) |
Conversions
std::strong_ordering
is the strongest of the three comparison categories: it is not implicitly-convertible from any other category and is implicitly-convertible to the other two.
operator partial_ordering
|
implicit conversion to std::partial_ordering (public member function) |
std::strong_ordering::operator partial_ordering
constexpr operator partial_ordering() const noexcept; |
Return value
std::partial_ordering::less
if v
is less
, std::partial_ordering::greater
if v
is greater
, std::partial_ordering::equivalent
if v
is equal
or equivalent
.
operator weak_ordering
|
implicit conversion to std::weak_ordering (public member function) |
std::strong_ordering::operator weak_ordering
constexpr operator weak_ordering() const noexcept; |
Return value
std::weak_ordering::less
if v
is less
, std::weak_ordering::greater
if v
is greater
, std::weak_ordering::equivalent
if v
is equal
or equivalent
.
Comparisons
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.
These functions are not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::strong_ordering
is an associated class of the arguments.
The behavior of a program that attempts to compare a strong_ordering
with anything other than the integer literal 0
is undefined.
operator==operator<operator>operator<=operator>=operator<=>
|
compares with zero or a strong_ordering (function) |
operator==
friend constexpr bool operator==(strong_ordering v, /*unspecified*/ u) noexcept; |
(1) | |
friend constexpr bool operator==(strong_ordering v, strong_ordering w) noexcept = default; |
(2) |
Parameters
v, w | - | std::strong_ordering values to check |
u | - | an unused parameter of any type that accepts literal zero argument |
Return value
true
if
v
is
equivalent
or
equal
,
false
if
v
is
less
or
greater
true
if both parameters hold the same value,
false
otherwise. Note that
equal
is the same as
equivalent
.
operator<
friend constexpr bool operator<(strong_ordering v, /*unspecified*/ u) noexcept; |
(1) | |
friend constexpr bool operator<(/*unspecified*/ u, strong_ordering v) noexcept; |
(2) |
Parameters
v | - | a std::strong_ordering value to check |
u | - | an unused parameter of any type that accepts literal zero argument |
Return value
true
if
v
is
less
, and
false
if
v
is
greater
,
equivalent
, or
equal
true
if
v
is
greater
, and
false
if
v
is
less
,
equivalent
, or
equal
operator<=
friend constexpr bool operator<=(strong_ordering v, /*unspecified*/ u) noexcept; |
(1) | |
friend constexpr bool operator<=(/*unspecified*/ u, strong_ordering v) noexcept; |
(2) |
Parameters
v | - | a std::strong_ordering value to check |
u | - | an unused parameter of any type that accepts literal zero argument |
Return value
true
if
v
is
less
,
equivalent
, or
equal
, and
false
if
v
is
greater
true
if
v
is
greater
,
equivalent
, or
equal
, and
false
if
v
is
less
operator>
friend constexpr bool operator>(strong_ordering v, /*unspecified*/ u) noexcept; |
(1) | |
friend constexpr bool operator>(/*unspecified*/ u, strong_ordering v) noexcept; |
(2) |
Parameters
v | - | a std::strong_ordering value to check |
u | - | an unused parameter of any type that accepts literal zero argument |
Return value
true
if
v
is
greater
, and
false
if
v
is
less
,
equivalent
, or
equal
true
if
v
is
less
, and
false
if
v
is
greater
,
equivalent
, or
equal
operator>=
friend constexpr bool operator>=(strong_ordering v, /*unspecified*/ u) noexcept; |
(1) | |
friend constexpr bool operator>=(/*unspecified*/ u, strong_ordering v) noexcept; |
(2) |
Parameters
v | - | a std::strong_ordering value to check |
u | - | an unused parameter of any type that accepts literal zero argument |
Return value
true
if
v
is
greater
,
equivalent
, or
equal
, and
false
if
v
is
less
true
if
v
is
less
,
equivalent
, or
equal
, and
false
if
v
is
greater
operator<=>
friend constexpr strong_ordering operator<=>(strong_ordering v, /*unspecified*/ u) noexcept; |
(1) | |
friend constexpr strong_ordering operator<=>(/*unspecified*/ u, strong_ordering v) noexcept; |
(2) |
Parameters
v | - | a std::strong_ordering value to check |
u | - | an unused parameter of any type that accepts literal zero argument |
Return value
v
.
greater
if
v
is
less
,
less
if
v
is
greater
, otherwise
v
.
Example
See also
(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 all 6 operators, is not substitutable, and allows incomparable values (class) |
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