std::strong_equality
Defined in header <compare> | ||
|---|---|---|
class strong_equality; | (since C++20) |
The class type std::strong_equality is the result type of a three-way comparison that.
- admits only equality and inequality comparisons (no less-than/greater-than)
- 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.
Constants
The type std::strong_equality has four valid values, implemented as const static data members of its type:
| Member constant | Definition |
|---|---|
| equivalent(inline constexpr)
[static] | a valid value of the type std::strong_equality indicating equality (public static member constant) |
| equal(inline constexpr)
[static] | a valid value of the type std::strong_equality indicating equality (public static member constant) |
| nonequivalent(inline constexpr)
[static] | a valid value of the type std::strong_equality indicating non-equality (public static member constant) |
| nonequal(inline constexpr)
[static] | a valid value of the type std::strong_equality indicating non-equality (public static member constant) |
Conversions
std::strong_equality is implicitly-convertible to std::weak_equality, and std::strong_ordering is implicitly-convertible to strong_equality.
| operator weak_equality | implicit conversion to std::weak_equality (public member function) |
std::strong_equality::operator weak_equality
constexpr operator weak_equality() const noexcept; |
Return value
std::weak_equality::equivalent if v is equivalent or equal, std::weak_equality::nonequivalent if v is nonequivalent or nonequal.
Comparisons
Comparison operators are defined between values of this type and literal 0. This supports the expressions a <=> b == 0 and a <=> b != 0 used to convert the result of a three-way comparison operator to a boolean relationship; see std::is_eq and std::is_neq.
The behavior of a program that attempts to compare a strong_equality with anything other than the integer literal 0 is undefined.
| operator==operator!=operator<=> | compares with zero (function) |
operator==
friend constexpr bool operator==(strong_equality v, /*unspecified*/ u) noexcept; friend constexpr bool operator==(/*unspecified*/ u, strong_equality v) noexcept; |
Parameters
| v | - | a std::strong_equality value 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 nonequivalent or nonequal.
operator!=
friend constexpr bool operator!=(strong_equality v, /*unspecified*/ u) noexcept; friend constexpr bool operator!=(/*unspecified*/ u, strong_equality v) noexcept; |
Parameters
| v | - | a std::strong_equality value to check |
| u | - | an unused parameter of any type that accepts literal zero argument |
Return value
false if v is equivalent or equal, and true if v is nonequivalent or nonequal.
operator<=>
friend constexpr strong_equality operator<=>(strong_equality v, /*unspecified*/ u) noexcept; friend constexpr strong_equality operator<=>(/*unspecified*/ u, strong_equality v) noexcept; |
Parameters
| v | - | a std::strong_equality value to check |
| u | - | an unused parameter of any type that accepts literal zero argument |
Return value
v.
Example
See also
|
(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 all 6 operators, is not substitutable, and allows incomparable values (class) |
|
(C++20) | the result type of 3-way comparison that supports only equality/inequality and is not substitutable (class) |
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