C++ concepts: EqualityComparable

 

C++

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C++ concepts

Basic
DefaultConstructible CopyAssignable CopyConstructible	MoveAssignable (C++11) MoveConstructible (C++11) Destructible
Library-Wide
EqualityComparable LessThanComparable Swappable (C++11) ValueSwappable (C++11)	NullablePointer (C++11) Hash (C++11) Allocator
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Other
CharTraits pos_type off_type Clock (C++11) BitmaskType	UnaryTypeTrait (C++11) BinaryTypeTrait (C++11) TransformationTrait (C++11) TrivialClock (C++11) LiteralType (C++11)

 

The type must work with == operator and the result should have standard semantics.

Requirements

The type T satisfies EqualityComparable if

Given

• a, b, and c, expressions of type T or const T

The following expressions must be valid and have their specified effects

Expression	Return type	Requirements
a == b	implicitly convertible to bool	Establishes equivalence relation with the following properties: For all values of a, a == a yields true. If a == b, then b == a If a == b and b == c, then a == c

Notes

To satisfy this requirement, types that do not have built-in comparison operators have to provide a user-defined operator==

For the types that are both EqualityComparable and LessThanComparable, the C++ standard library makes a distinction between equality, which is the value of the expression a == b and equivalence, which is the value of the expression !(a < b) && !(b < a).