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digitalmars.D.bugs - [Issue 1245] New: static foreach shouldn't define new scope and introduce new variables

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=1245

           Summary: static foreach shouldn't define new scope and introduce
                    new variables
           Product: D
           Version: 1.014
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: baryluk mpi.int.pl


import std.stdio;

void Code(x...)() {
        foreach (i, xi; x) {
                static if (xi != 0) { // dosn't works, see below
              //static if (x[i] != 0) { // workaround
                        writefln(xi);
                }
        }
}


void main() {
        alias Code!(1, 6, 0, 2, 5) c;
        c();
}

// staticforeachif.d(5): Error: expression xi != 0 is not constant 
// or does not evaluate to a bool

with workaround, it works, and display:
1
6
2
5
as needed

Imho foreach over tupple shouldn't introduce new scope and variables xi,
but as static if be in the same scope (if needed you always can add { .. }
and xi (second parameter in foreach), should be actually alias to x[i]

I'm using this in optimalisation of general code generators.


--
May 23 2007
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=1245


smjg iname.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |smjg iname.com




------- Comment #1 from smjg iname.com  2007-05-25 04:48 -------
Huh?  What is a "static foreach"?  If there's any reference to it in the spec,
it isn't obvious.


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May 25 2007
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------- Comment #2 from baryluk mpi.int.pl  2007-05-25 08:05 -------
http://www.digitalmars.com/d/tuple.html Looping section.
Foreach over tuple works like static foreach, and it is unrolled in compile
time.


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May 25 2007
prev sibling next sibling parent d-bugmail puremagic.com writes:
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smjg iname.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid




------- Comment #3 from smjg iname.com  2007-05-25 11:49 -------
I see.

But I'm not sure I see how it would work to make foreach not define a scope in
such circumstances.  OTOH, I agree that xi should be recognised as constant.


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May 25 2007
prev sibling next sibling parent d-bugmail puremagic.com writes:
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shro8822 uidaho.edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |shro8822 uidaho.edu




------- Comment #4 from shro8822 uidaho.edu  2007-05-25 12:17 -------
The issue I have is that int the foreach loop the value of i gets pushed onto
the stack. (I was looking at the ASM dump from DMD linux)

foreach(i, j; T!(1,2,3)
{
   asm{nop;};
} 

should compeile to
nop;
nop;
nop;


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May 25 2007
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------- Comment #5 from baryluk mpi.int.pl  2007-05-29 00:27 -------
Another example:

module staticforeach_switch;

import std.stdio;

template Tuple(E...) { alias E Tuple; }
alias Tuple!(101.0, 102.0, 103.0, 104.0) coef;

double f(int l, double x) {
   switch (l) {
     foreach (i, a_i; coef) {
        case i:
            //return x*a_i; // compiles and gives garbage
            return x*coef[i]; // works
      }
        default:
            assert(0);
   }
   assert(0);
}

void main() {
        writefln(f(3, 2.0)); // 2*104 = 208
}


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May 28 2007
prev sibling next sibling parent d-bugmail puremagic.com writes:
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--- Comment #6 from Witold Baryluk <baryluk smp.if.uj.edu.pl> 2009-11-18
21:41:58 PST ---
I just tested this both my codes (from "Description" and "Comment 5") in DMD
2.032, and they works correctly! (only switch isn't full optimal in asm, but
this not conected with this bug).

BCS's example with nop's is also not optimal, there are some operations on EBP
register:
        mov    dword ptr -034h[EBP],1
        nop
        mov    dword ptr -02Ch[EBP],2
        nop
        mov    dword ptr -024h[EBP],3
        nop
        mov    dword ptr -01Ch[EBP],5
        nop
        mov    dword ptr -014h[EBP],6
        nop
        mov    dword ptr -0Ch[EBP],7
        nop


I don't remember any changelog entry mentioning anything about foreach over
tuples... Anyone want to enlighten me? :) And what about DMD 1.x?

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prev sibling parent d-bugmail puremagic.com writes:
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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bearophile_hugs eml.cc
         Resolution|                            |FIXED


--- Comment #7 from bearophile_hugs eml.cc 2010-04-12 17:52:10 PDT ---
This is now fixed in DMD 1.058 and 2.043.

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Apr 12 2010