http://d.puremagic.com/issues/show_bug.cgi?id=10712

           Summary: Compiletime foreach loop
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: temtaime@gmail.com


--- Comment #0 from Temtaime <temtaime@gmail.com> 2013-07-25 01:09:52 PDT ---
Sometimes it's neccessary to organize compiletime loop/unroll another loop for better perfomance.

I'd make that simple template:

template IndexTuple(int e, int s = 0, T...) {
    static if(s == e)
        alias IndexTuple = T;
    else
        static if(s > e)
            alias IndexTuple = IndexTuple!(e, s - 1, T, s);
        else
            alias IndexTuple = IndexTuple!(e, s + 1, T, s);
}

Use:
foreach(idx; IndexTuple!10)
writeln(idx); // prints 0, 1, ..., 9

foreach(idx; IndexTuple!(10, 2))
writeln(idx); // prints 2, 3, ..., 9

foreach(idx; IndexTuple!-10)
writeln(idx); // prints 0, -1, ..., -9

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monarchdodra@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |monarchdodra@gmail.com


--- Comment #1 from monarchdodra@gmail.com 2013-07-25 03:12:47 PDT ---
(In reply to comment #0)
> Sometimes it's neccessary to organize compiletime loop/unroll another loop for better perfomance.
> 
> I'd make that simple template:
> 
> template IndexTuple(int e, int s = 0, T...) {
>     static if(s == e)
>         alias IndexTuple = T;
>     else
>         static if(s > e)
>             alias IndexTuple = IndexTuple!(e, s - 1, T, s);
>         else
>             alias IndexTuple = IndexTuple!(e, s + 1, T, s);
> }
> 
> Use:
> foreach(idx; IndexTuple!10)
> writeln(idx); // prints 0, 1, ..., 9
> 
> foreach(idx; IndexTuple!(10, 2))
> writeln(idx); // prints 2, 3, ..., 9
> 
> foreach(idx; IndexTuple!-10)
> writeln(idx); // prints 0, -1, ..., -9

It think this already exists in phobos somewhere, though I don't remember where though, and it probably wasn't good for public use.

In any case, I think the useage should more closely resemble what iota does.
For example:
IndexTuple!(2, 10)) vs IndexTuple!(10, 2))
or
IndexTuple!(0, -10, -1)) vs IndexTuple!(0, -10))

Arguably, iota accepts "iota(10)", but I (and others) think that is a retarded
idea, when typing "iota(0, 10)", is just and easy. I think we should avoid
making the same mistakes.

Also, it should be parameterizable on iteration type. Here is a rough sketch of an implementation that does this.

import std.stdio, std.traits;

template IndexTuple(alias l, alias h)
{
    alias IndexTuple = IndexTupleImpl!(l, h, 1);
}
template IndexTuple(alias l, alias h, alias inc)
{
    alias IndexTuple = IndexTupleImpl!(l, h, inc);
}

template IndexTupleImpl(alias l, alias h, alias inc, T...)
{
    alias E = CommonType!(l, h, inc);
    static if (inc == 0)
        static assert(0, "increment must be non-0");
    else static if (inc > 0 && l >= h)
        alias IndexTupleImpl = T;
    else static if(inc < 0 && l <= h)
        alias IndexTupleImpl = T;
    else
        alias IndexTupleImpl = IndexTupleImpl!(cast(E)(l + inc), h, inc, T, l);
}

void main()
{
    foreach(idx; IndexTuple!(0, 0))
    write(idx, ' '); // prints
    writeln();

    foreach(idx; IndexTuple!(0, 10))
    write(idx, ' '); // prints 0, 1, ..., 9
    writeln();

    foreach(idx; IndexTuple!(2, 10))
    write(idx, ' '); // prints 2, 3, ..., 9
    writeln();

    foreach(idx; IndexTuple!(0, -10, -1))
    write(idx, ' '); // prints 0, -1, ..., -9
    writeln();

    foreach_reverse(idx; IndexTuple!(-9, 1))
    write(idx, ' '); // prints 0, -1, ..., -9
    writeln();

    foreach(idx; IndexTuple!(0.5, 10))
    write(idx, ' '); // prints 0.5, 1.5, ..., 9.5
    writeln();

    foreach(idx; IndexTuple!(0, 1, 0.1))
    write(idx, ' '); // prints 0 0.1 ... 0.9
    writeln();

    foreach(idx; IndexTuple!('a', cast(char)('z' + 1), cast(char)1))
    write(idx, ' '); // prints a b ... z
    writeln();
}

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bearophile_hugs@eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs@eml.cc


--- Comment #2 from bearophile_hugs@eml.cc 2013-07-25 03:52:36 PDT ---
Dupe of Issue 4085 ?

> Arguably, iota accepts "iota(10)", but I (and others) think that is a retarded
> idea, when typing "iota(0, 10)", is just and easy. I think we should avoid
> making the same mistakes.

I requested that to Andrei. And I still think it's a good idea, it comes from Python iterations:

>>> range(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Discussing iota(10) is off topic here, but if you want you can explain here or
in D.learn.

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--- Comment #3 from bearophile_hugs@eml.cc 2013-07-25 03:58:35 PDT ---
(In reply to comment #2)

> >>> range(10)
> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
> 
> Discussing iota(10) is off topic here, but if you want you can explain here or
> in D.learn.

In D the single argument iota allows you to write UFCS chains like:

....reduce!(...).iota....

If you require the zero it breaks the linearity, and the zero is very common:

0.iota(....reduce!(...))....

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monarchdodra@gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |DUPLICATE


--- Comment #4 from monarchdodra@gmail.com 2013-07-25 04:11:02 PDT ---
(In reply to comment #2)
> Dupe of Issue 4085 ?

Looks like it. I also like the name "Iota!(0, 10, 2)": Imediatly clear.

> > Arguably, iota accepts "iota(10)", but I (and others) think that is a retarded
> > idea, when typing "iota(0, 10)", is just and easy. I think we should avoid
> > making the same mistakes.
> 
> I requested that to Andrei. And I still think it's a good idea, it comes from Python iterations:
> 
> >>> range(10)
> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
> 
> Discussing iota(10) is off topic here, but if you want you can explain here or
> in D.learn.

I think I remember a thread about this. But if there is existing reasons for doing it that way, I'm not going to go against it.

(In reply to comment #3)
> (In reply to comment #2)
> 
> > >>> range(10)
> > [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
> > 
> > Discussing iota(10) is off topic here, but if you want you can explain here or
> > in D.learn.
> 
> In D the single argument iota allows you to write UFCS chains like:
> 
> ....reduce!(...).iota....

That's a good point.

Closing as dup.

*** This issue has been marked as a duplicate of issue 4085 ***

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