On Wednesday, 1 April 2015 at 18:13:15 UTC, Ali Çehreli wrote:
On 04/01/2015 10:57 AM, Dzugaru wrote:
> ElementType!S aggregate(alias func, S)(S list, ElementType!S
accum =
> ElementType!S.init)
> if(is(typeof(func(accum, accum)) == typeof(accum))) {
[...]
> }
I can't explain exactly why that doesn't work.
However, I've discovered a number of times that reducing the
dependency between template parameters helps. Instead of using
ElementType!S in the parameter list, introduce a third one (E),
which you check in the template constraint:
ElementType!S aggregate(alias func, S, E)(S list, E accum =
E.init)
if(is (E == ElementType!S) && // <-- ADDED
is(typeof(func(accum, accum)) == typeof(accum))) {
// ...
}
Now it works.
Ali
This code does work when you provide second (non-default)
argument to function, and doesn't if you do not (no way it can
deduce E solely from checks I assume).
My version, in constract, works when you do not provide second
argument and doesn't if you do.