Why D const is annoying

[Timon Gehr]

On 12/10/2011 12:27 PM, Walter Bright wrote:
> On 12/10/2011 3:17 AM, Mehrdad wrote:
>> Yup, I started using it as soon as Timon mentioned it (thanks for the
>> suggestion!).
>> But I was referring to the bug, not to the workaround. :)
>
> It isn't a bug, it is designed to work that way.

I think the design might contain a bug and should be revisited.

> The type of the
> instantiation is based on the argument types, not the parameter types.
> (Note that "2" is the argument and "N" is the parameter.)
>
> Hence the message:
>
> Error: cannot implicitly convert expression (m) of type Matrix!(int,2)
> to Matrix!(int,N)
>
>
>> (I don't understand
>> why Matrix!(int, cast(int)1) is considered a different instantiation,
>> when it
>> can't even be instantiated...)
>
> Yes, it can be instantiated. But it cannot be implicitly converted to
> type Matrix!(int, cast(uint)1) because they are different types.

What is the benefit of having this apparent mis-feature?
It is similar to having the calling conventions of a function depend on 
the actual arguments instead of the formal parameters. It would likely 
result in a segmentation fault. For templates, luckily the compiler only 
blows up with an error message in counter-intuitive ways. I think there 
must be a very good reason to keep this.