ProtoObject and comparison for equality and ordering

[Seb]

On Wednesday, 15 May 2019 at 00:08:10 UTC, Andrei Alexandrescu 
wrote:
> On 5/14/19 12:36 AM, Seb wrote:
>> On Tuesday, 14 May 2019 at 21:06:05 UTC, Mike Franklin wrote:
>>> On Tuesday, 14 May 2019 at 20:36:08 UTC, Eduard Staniloiu 
>>> wrote:
>>>
>>>> Should `opCmp` return a float?
>>>>
>>>> The reason: when we attempt to compare two types that aren't 
>>>> comparable (an unordered relationship) we can return 
>>>> float.NaN. Thus we can differentiate between a valid -1, 0, 
>>>> 1 and an invalid float.NaN comparison.
>>>
>>> Seems like a job for an enum, not a float or an integer.
>>>
>>> Mike
>> 
>> +1 for enum. As far as I can see you only have four actual 
>> states:
>> 
>> lower, equal, higher, nonComparable
>
> This won't work because the result of opCmp is compared against 
> zero. Using a floating point number is likely to be more 
> efficient.

A DIP should cite real evidence/data though.

Also, note that all other cases except comparing against NaN 
require more instructions with a floating point number:

https://d.godbolt.org/z/lwzBVn