On Fri, Aug 6, 2010 at 21:54, Peter Alexander
<[email protected]>wrote:
> Is this a bug, or a limitation of how operator overloads handle generic
> operands?
>
> struct Vec(int N) {}
>
> struct Mat(int M, int N)
> {
> Vec!(M) opBinary(string op)(in Vec!(N) rhs)
> {
> return Vec!(M)();
> }
> }
>
> void main()
> {
> Vec!(3) v;
> Mat!(3, 3) m;
>
> Vec!(3) x = m * v; // Error: incompatible types for m * v
> Vec!(3) y = m.opBinary("*")(v); // Works
> }
>
> Note that if you change the operator signature to:
>
> Vec!(3) opBinary(string op)(in Vec!(3) rhs)
>
> then the first statement also compiles, but of course this makes the
> program incorrect.
>
> Is this a bug or a language limitation?
>
I don't know how to classify it. You can help the compiler by defining
aliases to types:
struct Mat(int M, int N)
{
alias Vec!N ColumnType;
alias Vec!M RowType;
RowType opBinary(string op)(ColumnType rhs)
{
return RowType();
}
}
And then it works!
A nice side-effect is that, given an M, you now have M.ColumType and
M.RowType exposed, to do what you want.
Maybe another possibility is to use templates constraints?
Philippe
