C++ named requirements: LessThanComparable
The type must work with < operator and the result should have standard semantics.
Requirements
The type T satisfies LessThanComparable if
Given
a
,b
, andc,
expressions of typeT
orconst T
The following expressions must be valid and have their specified effects:
Expression | Return type | Requirements |
---|---|---|
a < b | implicitly convertible to bool | Establishes strict weak ordering relation with the following properties * For all a , !(a < a) * If a < b then !(b < a) * If a < b and b < c then a < c * Defining equiv(a, b) as !(a < b) && !(b < a) , if equiv(a, b) and equiv(b, c) , then equiv(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)
.