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.col...@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
<schvei...@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.
