ProtoObject and comparison for equality and ordering

[Andrei Alexandrescu]

On 5/14/19 1:57 AM, Seb wrote:
> Well, you already plan to change the compiler, so changing it to create 
> a different opCmp lowering when it sees this special enum wouldn't be so 
> hard, no?

The DIP's charter does not include modifying opCmp.

> i.e. if both opCmps return a special CompEnum, do sth. like this:
> 
> a < b => a.opCmp(b) == lowerCmp
> ...
> 
> 
> There's no price to pay this way.

Well there would be in some instances. People often implement 
comparisons as a - b currently, where a and b are int expressions. That 
would need to become...

return a < b ? lowerCmp : a > b ? upperCmp : equivCmp;

That's definitely liable to be worse for those cases.

Overall: I dream of a D landscape whereby this is enough of a problem to 
deserve discussion, a DIP, review, and implementation. As things are 
there are sufficient things to discuss and improve in D to make this 
exchange ironic.