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digitalmars.D.bugs - [Issue 8576] New: unions call destructors of all their fields

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8576

           Summary: unions call destructors of all their fields
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc



Title: 
Component: DMD
Severity: major
Code number: 
Keywords: 
Outcome: wrong_code
Is done: no


import std.stdio;
struct Foo1 {
    ~this() { writeln("Foo1.dtor"); }
}
struct Foo2 {
    ~this() { writeln("Foo2.dtor"); }
}
struct Foo3 {
    ~this() { writeln("Foo3.dtor"); }
}
union U {
    Foo1 f1;
    Foo2 f2;
    Foo3 f3;
}
void main() {
    U u;
}


Output:

Foo3.dtor
Foo2.dtor
Foo1.dtor



A comment by Andrei Alexandrescu:
http://forum.dlang.org/thread/cqimoyzvlanjbmuzbtiy forum.dlang.org#post-k0eclr:242093:241:40digitalmars.com


 That's pretty surprising. "Major bug" doesn't begin to describe it.
 Unions should call no constructors and no destructors.


-------------------------

But maybe there are alternative solutions. Elsewhere I have suggested an
*optional* standard method for unions, to be called at run-time by the garbage
collector to increase its precision when it has to deal with union instances.

When such activeField() method is defined, it may be called at the end of the
scope where the union is defined:


struct Foo {}
struct Bar {}

struct Spam {
    bool isBar;

    union {
        Foo f;
        Bar b;

        size_t activeField() {
            return isBar ? 1 : 0;
        }
    }
}

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Aug 21 2012
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8576


bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Platform|All                         |x86
         OS/Version|All                         |Windows
           Severity|normal                      |major


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Aug 21 2012
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8576


Maxim Fomin <maxim maxim-fomin.ru> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |maxim maxim-fomin.ru
         Resolution|                            |DUPLICATE



---
*** This issue has been marked as a duplicate of issue 4421 ***

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May 18 2013