11 Classes [class]

A secondary comparison operator is a relational operator ([expr.rel]) or the != operator.

A defaulted operator function ([over.binary]) for a secondary comparison operator @ shall have a declared return type bool.

The operator function with parameters x and y is defined as deleted if

• (2.1)
  a first overload resolution ([over.match]), as applied to x @ y,
  • (2.1.1)
    does not result in a usable candidate, or
  • (2.1.2)
    the selected candidate is not a rewritten candidate, or
• (2.2)
  a second overload resolution for the expression resulting from the interpretation of x @ y using the selected rewritten candidate ([over.match.oper]) does not result in a usable candidate (for example, that expression might be (x <=> y) @ 0), or
• (2.3)
  x @ y cannot be implicitly converted to bool.

In any of the two overload resolutions above, the defaulted operator function is not considered as a candidate for the @ operator.

Otherwise, the operator function yields x @ y.