Why D const is annoying

[Mehrdad]

On 12/10/2011 2:46 AM, Timon Gehr wrote:
> On 12/10/2011 11:18 AM, Mehrdad wrote:
>> ... and another...
>>
>> struct S(T, int N)
>> { public auto opBinary(string op)(in S!(T, N) other) const { return
>> this; } }
>> void main() { S!(int, 1) m; m = m * m; }
>>
>> Error: 'm' is not of arithmetic type, it is a Matrix!(int,1)
>> Error: 'm' is not of arithmetic type, it is a Matrix!(int,1)
>
> It is unrelated to const, this gives the same error.
> struct S(T, int N)
> { public auto opBinary(string op)(S!(T, N) other) { return this; } }
> void main() { S!(int, 1) m; m = m * m; }
Yeah, I've complained about const before, but I never said this one was 
related. :P I just had the word 'const' in there because it was in my 
original code and I forgot to take it out.

> And this works:
>
> struct S(T, int N)
> { public auto opBinary(string op)(in S other) const { return this; } }
> void main() { S!(int, 1) m; m = m * m; }
>
> You have to make sure that the signature of your template actually 
> compiles. Maybe the compiler should emit a diagnostic for that case.
Sure, but what's wrong with my version that makes it not compile?

> If you blame all your compile errors on const, I can understand why 
> you think its design is broken.

Not _all_ of them (e.g. I figured this one wasn't one of them), but yes, 
a significant fraction of them that I've seen, only a few of which I've 
been in the mood to post. :)
So yeah, that's why I've come to the conclusion that it's broken.