opBinary failes with templates

[Asger Dam Hoedt]

2011/7/27 Steven Schveighoffer <schveiguy at yahoo.com>

> On Wed, 27 Jul 2011 15:48:24 -0400, Asger Dam Hoedt <asgerhoedt at gmail.com>
> wrote:
>
>  Hey
>>
>> I've very recently started playing around with D, but I seem to have hit
>> my
>> head against a bug in dmd. I want to create a Vector class templated with
>> its dimension. This works fine until I try to overload the + operator for
>> my
>> vector and use it. I then get the error
>>
>> Error: incompatible types for ((vec) + (vec)): 'Vector!(3)' and
>> 'Vector!(3)'
>>
>> I've boiled it down to a small example
>>
>> struct Vector(int D) {
>>    float es[D];
>>
>> public:
>>    this(immutable float x, immutable float y, immutable float z) {
>>        es[0] = x; es[1] = y; es[2] = z;
>>    }
>>
>>    Vector!(D) opBinary(string s)(immutable Vector!(D) rhs) if (s == "+") {
>>        Vector!(D) ret;
>>        for(int i = 0; i < D; ++i)
>>            ret.es[i] = es[i] + rhs.es[i];
>>        return ret;
>>    }
>>
>> }
>>
>> alias Vector!(3) Vector3;
>>
>> void main() {
>>    Vector3 vec = Vector3(0,1,2);
>>    vec = vec.opBinary!("+")(vec); // This works fine
>>    vec = vec + vec; // This line fails miserably
>> }
>>
>> If I replace the template argument in for the argument rhs with 3, then
>> everything works, but that's not really a nice solution :)
>>
>> Is it me trying to use templates in a way they aren't meant to be used or
>> is
>> this a bug in dmd? If it is a bug, does anyone have an idea how to solve
>> this? I wouldn't mind fixing it in dmd myself, I just need some
>> guidelines.
>>
>
> It is a bug, someone just brought up almost exactly this problem in
> d.learn.
>
> http://www.digitalmars.com/**webnews/newsgroups.php?art_**
> group=digitalmars.D.learn&**article_id=28455<http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D.learn&article_id=28455>
>
> The proper workaround (and actually, the cleaner solution) is to use Vector
> and not Vector!D.  Inside a template, the name of the template is the same
> as if you invoked the template with the same template parameters.
>
> If you actually do need a different value for D, I'm not sure what works.
>
> -Steve
>

Oh nice. I'll go with the clean solution then and disregard the bug for now.
Thanks for the quick help.

/asger
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