On Wednesday, 28 September 2016 at 04:02:59 UTC, Walter Bright
wrote:
The limitations are deliberate based on the idea that
comparison operators need to be consistent and predictable, and
should have a close relationship to the mathematical meaning of
the operators.
In Mathematics the comparison operators are also commonly used
for semi orders, which cannot be implemented by opCmp, because
opCmp has no way to indicate that two values are incomparable.
Interestingly the floating point types are semi ordered (due to
NaNs), and for those D has some (non-overridable and deprecated)
operators like !<, which would be easily extendable to any semi
order, whereas the suggested replacement (i.e. test for NaNs
manually) works only on floats.
