is() syntax (Re: operator new(): struct v. class)

[Don Clugston]

Kirk McDonald wrote:
> Bill Baxter wrote:
>> And why do we even need is() to do basic type comparisons anyway?
>> What's ambiguous about
>>    static if( MyType == OtherType ) {
>>         ...
>>    }
>> ?
>> I guess you could define a static opEquals, but A) that's useless 
>> enough that it could be outlawed B) it wouldn't take a type as an 
>> argument so it still wouldn't be ambiguous.
>>
>> --bb
> 
> It is ambiguous. Both sides of a comparison must be an expression, and 
> types are not expressions. Allowing that would mean you couldn't 
> determine whether 'MyType' is an expression or a type until after the 
> syntactic pass. This would break some cardinal rules about the ease with 
> which you can parse D code.

Ideally, I think, we'd have a merge between is() and typeof()/typeid()
static if (typeid(MyType)==typeid(OtherType)) {
}

There are quite a few cases where we have syntax which is completely different 
at run-time compared to compile compile-time, yet which do exactly the same 
thing. __traits and typeinfo seem to be awfully similar, for example.
If they were unified, CTFE could grab even more territory from templates.