www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.bugs - [Issue 10712] New: Compiletime foreach loop

reply d-bugmail puremagic.com writes:
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

-- 
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
Jul 25 2013
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=10712


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(); } -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jul 25 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=10712


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. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jul 25 2013
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=10712



--- 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!(...)).... -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jul 25 2013
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=10712


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 *** -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jul 25 2013