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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, and c, expressions of type T or const T

The following expressions must be valid and have their specified effects:

ExpressionReturn typeRequirements
a < bimplicitly convertible to boolEstablishes 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).

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, and c, expressions of type T or const T

The following expressions must be valid and have their specified effects:

ExpressionReturn typeRequirements
a < bimplicitly convertible to boolEstablishes 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).