On Tuesday, 3 June 2014 at 13:23:36 UTC, Steven Schveighoffer wrote:
> On Mon, 02 Jun 2014 17:25:24 -0400, John Colvin <john.loughran.colvin@gmail.com> wrote:
>
>> On Monday, 2 June 2014 at 20:23:12 UTC, Steven Schveighoffer wrote:
>>> On Mon, 02 Jun 2014 15:58:01 -0400, Steven Schveighoffer <schveiguy@yahoo.com> wrote:
>>>
>>>
>>>> I'm trying to think of a way to do this without loops, but not sure.
>>>
>>> I'm surprised, I looked for some kind of "apply" function like map, but just calls some function with each element in the range.
>>>
>>> Something like this would make this a 1 (2?) liner:
>>>
>>> if(i == t.length) writeln(t) else each!((x) => {t[i] = x; foo(i+1);})(iota(x.length));
>>>
>>> But I can't find a phobos primitive for each. Would have expected it in std.algorithm or std.functional?
>>>
>>> -Steve
>>
>> Its been discussed a few times. There were some objections (IIRC Walter thought that there was no significant advantage over plain foreach).
>
> Indeed, foreach is like such a construct:
>
> ... else each!((x) {t[i] = x; foo(i+1);})(iota(t.length));
> ... else foreach(x; 0 .. t.length) {t[i] = x; foo(i+1);}
>
> It's even shorter and clearer.
>
> I agree with Walter. Since such a construct by definition wouldn't return anything, you can't chain it. There really is little reason to have it.
>
> -Steve

It's more useful like this:


import std.algorithm, std.stdio, std.range;

template call(Funcs ...)
{
    auto call(T)(T val)
    {
        foreach(F; Funcs)
        {
            F(val);
        }
        return val;
    }
}

void doubleIt(ref int i)
{
    i *= 2;
}

void evalAll(R)(R r)
{
    foreach(v; r){}
}	

void main()
{
    [1,2,3,4].map!(call!(doubleIt, write))().evalAll(); //prints 2468
	
    assert([1,2,3,4].map!(call!doubleIt)().equal([2,4,6,8]));
}


Eager iteration and mapping functions that don't return anything useful are orthogonal.