http://d.puremagic.com/issues/show_bug.cgi?id=3825

           Summary: A bug-prone situation with AAs
           Product: D
           Version: 2.040
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: druntime
        AssignedTo: sean@invisibleduck.org
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2010-02-18 12:26:51 PST ---
import std.stdio;
void main() {
    string[] words = ["how", "are", "you", "are"];

    int[string] aa1;
    foreach (w; words)
        aa1[w] = ((w in aa1) ? (aa1[w] + 1) : 2);
    writeln(aa1); // Prints: [how:1,you:1,are:2]

    int[string] aa2;
    foreach (w; words)
        if (w in aa2)
            aa2[w]++;
        else
            aa2[w] = 2;
    writeln(aa2); // Prints: [how:2,you:2,are:3]
}

This can be a source of bugs in programs. I don't know if there are ways to help the programmer avoid this bug.

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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
                 CC|                            |yebblies@gmail.com
           Platform|x86                         |All
            Version|2.040                       |D1 & D2
         AssignedTo|nobody@puremagic.com        |yebblies@gmail.com
            Summary|A bug-prone situation with  |AAs entries are default
                   |AAs                         |initialized before the new
                   |                            |value is evaluated
         OS/Version|Windows                     |All
           Severity|normal                      |major


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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jmdavisProg@gmx.com


--- Comment #1 from yebblies <yebblies@gmail.com> 2012-02-03 18:35:00 EST ---
*** Issue 5021 has been marked as a duplicate of this issue. ***

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Jonathan M Davis <jmdavisProg@gmx.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |luka8088@owave.net


--- Comment #2 from Jonathan M Davis <jmdavisProg@gmx.com> 2012-05-09 00:21:06 PDT ---
*** Issue 8070 has been marked as a duplicate of this issue. ***

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--- Comment #3 from bearophile_hugs@eml.cc 2012-06-21 00:10:43 PDT ---
Yesterday I've wasted some hours to locate this problem again in one of my programs. I hope this bug will be fixed.

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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dawg@dawgfoto.de


--- Comment #4 from yebblies <yebblies@gmail.com> 2012-10-30 00:26:23 EST ---
*** Issue 7914 has been marked as a duplicate of this issue. ***

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Kenji Hara <k.hara.pg@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull


--- Comment #5 from Kenji Hara <k.hara.pg@gmail.com> 2013-01-11 07:12:36 PST ---
https://github.com/D-Programming-Language/dmd/pull/1465

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--- Comment #6 from bearophile_hugs@eml.cc 2013-01-12 08:58:03 PST ---
Hara, I am reading the discussions in Pull 1465, and I have to say I use this kind of code all the time:

aa[x]++;

It's very handy. It's similar to a Python defaultdict:

>>> from collections import defaultdict
>>> d = defaultdict(int)
>>> x = 'c'
>>> d[x] += 1
>>> d
defaultdict(<type 'int'>, {'a': 1})


If you disallow that If you disallow that, I will have tons of broken code. And I have to replace:

aa[x]++;

With:

if (x in aa)
    aa[x]++;
else
    a[x] = 0;

This makes D code longer, and it doesn't make it safer.

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--- Comment #7 from github-bugzilla@puremagic.com 2013-03-03 17:46:25 PST ---
Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/d5aac8cc2bcc43e8753d889eff8e005f5c7443ce
fix Issue 3825 - AAs entries are default initialized before the new value is
evaluated

https://github.com/D-Programming-Language/dmd/commit/4af794608d6a29a1b03216038bcab63658ea9d87 Merge pull request #1465 from 9rnsr/fix3825

Issue 3825 - AAs entries are default initialized before the new value is evaluated

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--- Comment #8 from bearophile_hugs@eml.cc 2013-03-03 18:42:38 PST ---
Woo, after more than three years now it seems to work correctly. Close?

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