No static fold in phobos ?

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On Friday, 27 November 2015 at 20:57:44 UTC, userabcABC123 wrote:
> That would work on an AliasSeq ?
> I'm surprised not to find one:
>
> eg:
>
> ~~~~~~~
> enum seq = AliasSeq!("aa", "bb");
> enum val = staticFold!((a,b)=>a~b, seq);
> static assert(val == "aabb");
> ~~~~~~~
>
> it works with foreach or a eponymous template that consumes the 
> sequence , but as said where is it in phobos ?

There's not much sense in a staticFold template that takes a 
function literal, as you can use regular functions in D at 
compile time. However, you need to use template "functions" for 
some things, so here's a simple way to do that:

template staticFold(alias f, List...)
if (List.length > 1)
{
	static if (List.length == 2)
	{
		alias staticFold = f!(List[0], List[1]);
	}
	else
	{
		alias staticFold = staticFold!(f, f!(List[0], List[1]), 
List[2..$]);
	}
}

enum cat(alias l, alias r) = l ~ r;

void main()
{
	assert(staticFold!(cat, [0], [1]) == [0, 1]);
	assert(staticFold!(cat, [0], [1], [2]) == [0, 1, 2]);
	assert(staticFold!(cat, [0], [1], [2], [3]) == [0, 1, 2, 3]);
	assert(staticFold!(cat, [0], 1, 2, 3, 4) == [0, 1, 2, 3, 4]);
}