[Issue 4421] New: Union propagates copy constructors and destructors over all members

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=4421

           Summary: Union propagates copy constructors and destructors
                    over all members
           Product: D
           Version: 2.041
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: accepts-invalid, spec
          Severity: major
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: rsinfu at gmail.com


--- Comment #0 from Shin Fujishiro <rsinfu at gmail.com> 2010-07-04 02:59:50 PDT ---
Copy constructor and destructor are invoked on every field of a union.  It must
be compile error to define a union containing any object which has a
copy-constructor and/or a destructor -- since calling cpctor or dtor on
'non-active members' leads to undefined behavior.

This program compiles:
--------------------
import std.stdio;
void main()
{
    U u, v;
    v = u;
}
union U
{
    R r;
    S s;
}
struct R
{
    this(this) { writeln("R : this(this)"); }
    ~this()    { writeln("R : ~this()"); }
}
struct S
{
    this(this) { writeln("S : this(this)"); }
    ~this()    { writeln("S : ~this()"); }
}
--------------------

And prints this lines:
--------------------
R : this(this)
S : this(this)
S : ~this()
R : ~this()
S : ~this()
R : ~this()
S : ~this()
R : ~this()
--------------------

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