Re: Template argument deduction from a function call question

[Dzugaru via Digitalmars-d]

On Wednesday, 1 April 2015 at 18:37:24 UTC, Ali Çehreli wrote:
On 04/01/2015 11:27 AM, Dzugaru wrote:
> 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.

Another attempt:

import std.range;

ElementType!S
aggregate(alias func, S, E = ElementType!S)(S list, E accum = 
E.init)
    if(is(typeof(func(accum, accum)) == typeof(accum)))
{
    foreach(ref e; list) {
        accum = func(accum, e);
    }

    return accum;
}

void main()
{
    auto min1 = aggregate!((a,  b) { return a < b ? a : b; 
})([2,4,1,3,5], int.max);
    auto min2 = aggregate!((a,  b) { return a < b ? a : b; 
})([2,4,1,3,5]);

    assert(min1 == 1);
    assert(min2 == 0);
}

Ali

This is perfect, many thanks. Didn't know I can use "=" in 
template parameter list.