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digitalmars.D.bugs - [Issue 4378] New: Array Literals as Default Field Initializers Shared Across Instances.

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=4378

           Summary: Array Literals as Default Field Initializers Shared
                    Across Instances.
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: dsimcha yahoo.com


--- Comment #0 from David Simcha <dsimcha yahoo.com> 2010-06-23 17:04:12 PDT ---
import std.stdio;

struct Foo {
    int[] bar = [1, 2, 3, 4, 5];
}

void main() {
    Foo foo;
    foo.bar[0] = 3;

    Foo foo2;
    writeln(foo2.bar);  // 3 2 3 2 5
}

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Jun 23 2010
next sibling parent d-bugmail puremagic.com writes:
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Jonathan M Davis <jmdavisProg gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |jmdavisProg gmail.com


--- Comment #1 from Jonathan M Davis <jmdavisProg gmail.com> 2010-06-23
17:17:27 PDT ---
I think that you mean

writeln(foo2.bar);  // 3 2 3 4 5

but regardless, it's definitely a bug.

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--- Comment #2 from David Simcha <dsimcha yahoo.com> 2010-06-23 17:45:44 PDT ---
Yeah, that's just a typo.

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--- Comment #3 from David Simcha <dsimcha yahoo.com> 2010-06-23 17:46:59 PDT ---
Forgot to mention, this also applies to classes, not just structs.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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nfxjfg gmail.com changed:

           What    |Removed                     |Added
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                 CC|                            |nfxjfg gmail.com


--- Comment #4 from nfxjfg gmail.com 2010-06-24 05:32:46 PDT ---
How is this supposed to work "correctly"? Hidden allocation of an array on the
heap every time a struct of that type is "constructed"? Disallow initializing
non-immutable, non-static array members?

This is not a bug, it's just D _works_. If you assign an array to a global
variable, of course it's shared by everyone. Dynamic arrays are reference
types. The "variable" being a struct initializer doesn't change this.

I think this really should be marked as INVALID.

(I'm sure it's somewhat confusing for programmers coming from C++ or Java.
Especially in Java, the array would be reconstructed every time the constructor
is called. Stuff like this _never_ happens in D: structs are always initialized
by what boils down to a memcpy.)

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--- Comment #5 from Jonathan M Davis <jmdavisProg gmail.com> 2010-06-24
10:07:27 PDT ---
bar is a member varible _not_ a class variable and should _not_ be global. As
such, two independently constructed variables of type Foo should have bars
which referenc totally separate arrays. If bar were static, then they'd be
shared, but it's not.

Now, if the second Foo were constructed by copying the first one, then sure,
that's going to result in both bars referencing the same array, and setting an
element of one will affect the other. However, in this case, both variables of
type Foo were constructed independently, so their bars should not point to the
same array.

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yebblies <yebblies gmail.com> changed:

           What    |Removed                     |Added
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                 CC|                            |yebblies gmail.com


--- Comment #6 from yebblies <yebblies gmail.com> 2010-06-25 01:24:21 PDT ---
I can't get dmd to find core.thread atm for some reason, but does the same
thing happen with tls globals?

eg.

import core.thread;
import std.stdio;

int[] x = [1, 2, 3];

void main()
{
    writeln(x);
    x[0] = 9;
    writeln(x);
    new Thread(&thread2);
}

void thread2()
{
    writeln(x);
}

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Jun 25 2010
prev sibling parent d-bugmail puremagic.com writes:
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yebblies <yebblies gmail.com> changed:

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


--- Comment #7 from yebblies <yebblies gmail.com> 2012-02-02 14:29:15 EST ---
*** This issue has been marked as a duplicate of issue 2947 ***

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Feb 01 2012