writeln(typeid(typeof(a.init))); // prints: int
?! You mean typeof(a) != typeof((typeof(a)).init) ?!
Ugh... I thought (int[2]).init was [0,0] and in general (T[n]).init was [(T.init) n times]
writeln(foo(a)); // test.d(14): Error: Array operation s + s not implemented
}
But now I don't know what's happening, because that trait correctly returns false, but the compiler generates a compile error at line 14 still. I think there's a new bug
I think your bug is this discrepancy between init's type and the original type. That needs a bug report by itself;
in a template constraint, any value is at its type .init value, not its runtype value (obvious in retrospect)
In your example {return s+s;} becomes {return 0+0;}, since the compiler wrongly infer (int[2]).init to be 0, a regular int.
And your __traits return true:
auto bar(T)(T t) { return __traits(compiles, {return t+t;});}
int[2] a;
writeln(bar(a)); // true!
Philippe