opCmp, [partial/total/pre]orders, custom floating point types etc.

[Timon Gehr via Digitalmars-d]

On 01/12/2016 10:02 PM, John Colvin wrote:
> On Tuesday, 12 January 2016 at 20:52:51 UTC, Timon Gehr wrote:
>> On 01/12/2016 07:27 PM, John Colvin wrote:
>>> ...
>>
>>
>> struct S{
>>     auto opCmp(S rhs){ return float.nan; }
>>     bool opEquals(S rhs){ return false; }
>> }
>>
>> unittest{
>>     S a,b;
>>     assert(!(a==b));
>>     assert(!(a<b));
>>     assert(!(a<=b));
>>     assert(!(a>b));
>>     assert(!(a>=b));
>> }
>
> what about classes and Object.opCmp?

You can introduce a new opCmp signature in your subclass, but == is 
enforced to be reflexive for class objects. So this approach only really 
works for structs. (And for structs, it is obviously a hack.)