On Saturday, 13 May 2017 at 14:17:24 UTC, H. S. Teoh wrote:
Andrei specifically stated before that opCmp may model a partial order, i.e., returning 0 may indicate "not comparable" rather than "equal". And this is why opEquals is necessary: to distinguish between "not comparable" and "equal".
As others have pointed out, that seems wrong. However, returning float.nan does make a bit of sense. Given a nan return value, a <= b and a >= b will both be false.
