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digitalmars.D.bugs - [Issue 4603] New: array(iota(1, 0)) error

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           Summary: array(iota(1, 0))  error
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc


--- Comment #0 from bearophile_hugs eml.cc 2010-08-09 07:49:55 PDT ---
This generates an 'Access Violation' with dmd 2.048beta:


import std.range;
void main() {
    array(iota(1, 0));
}


The expected result of this array() is an empty dynamic array of signed
integers.

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kennytm gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kennytm gmail.com
         OS/Version|Windows                     |All


--- Comment #1 from kennytm gmail.com 2010-08-09 10:40:09 PDT ---
If you write

---

import std.range;
import std.stdio;
void main() {
    foreach (a; iota(1, 0)) {
        writeln(a);
    }
}

---

the program will never stop writing. Looks like an integer overflow bug.

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--- Comment #2 from kennytm gmail.com 2010-08-09 11:03:43 PDT ---
Created an attachment (id=707)
Patch for range.d to produce an empty range when pastLast <= current.

This patch produces an empty range when pastLast <= current. But this is
inconsistent with the behavior of floating point iota ranges.

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--- Comment #3 from kennytm gmail.com 2010-08-09 11:08:17 PDT ---
Created an attachment (id=708)
Patch for range.d to throw when pastLast <= current.

This patch simply enforces pastLast > current, so it is consistent with the
floating point iota range. But it may be less useful.

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David Simcha <dsimcha yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dsimcha yahoo.com


--- Comment #4 from David Simcha <dsimcha yahoo.com> 2010-08-19 17:07:09 PDT ---
Fixed in changeset 1901.  I chose to throw in this case.  The proper way to
create an empty range would be to do iota(0, 0), or iota(1, 1).  The main
reason for this choice was consistency with array slicing.  For example, if
bounds checking is enabled, array[3..2] throws a RangeError.

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--- Comment #5 from bearophile_hugs eml.cc 2010-08-19 17:44:23 PDT ---
Throwing? No, look at Python:

 range(1, 0)
[] It needs to return an empty range. This: foreach (i; iota(1, 0)) is the same as: foreach (i; 1 .. 0) Or: for (int i = 1; i < 0; i++) It's like an empty loop. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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--- Comment #6 from bearophile_hugs eml.cc 2010-08-19 17:49:22 PDT ---
And by the way, in Python This produces an empty string slice:

 "abcdefg"[3:2]
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David Simcha <dsimcha yahoo.com> changed:

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


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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |


--- Comment #7 from bearophile_hugs eml.cc 2010-08-20 05:16:23 PDT ---
Thank you for improving this bug. But I reopen the bug because I think raising
an error is the wrong design. As I have explained iota() is to be meant as the
ranges in for/foreach loops, so iota(1, 0) is like an empty loop, it's not an
error.

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Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |ASSIGNED
                 CC|                            |andrei metalanguage.com
         AssignedTo|nobody puremagic.com        |andrei metalanguage.com


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--- Comment #8 from bearophile_hugs eml.cc 2011-06-29 13:34:52 PDT ---
See also bug 6222

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Brad Anderson <eco gnuk.net> changed:

           What    |Removed                     |Added
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                 CC|                            |eco gnuk.net


--- Comment #9 from Brad Anderson <eco gnuk.net> 2012-04-19 18:41:12 PDT ---
This now seems to work as you want in DMD 2.059.  The following:

    import std.stdio, std.range;
    void main() {
        auto empty_array = array(iota(1, 0));
        writeln("type: ", typeof(empty_array).stringof,
                ", empty? ", empty_array.empty,
                ", contents: ", empty_array);
    }

Outputs:

    type: int[], empty? true, contents: []

I'd say it can be closed and marked RESOLVED now.

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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


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