C++ concepts: LessThanComparable

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

[edit] Requirements

The type T satisfies LessThanComparable if


  • 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 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

[edit] 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).