[Issue 9704] New: Destructor not called on function calls if postblit throws

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=9704

           Summary: Destructor not called on function calls if postblit
                    throws
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: johannespfau at gmail.com


--- Comment #0 from Johannes Pfau <johannespfau at gmail.com> 2013-03-12 11:35:39 PDT ---
See the attached testcase:

If the throw statement in B's postblit is commented we see the expected result:
A:this(this)
B:this(this)
A:~this
B:~this
B:~this
A:~this

The function call creates two copies, then the destructors are called for the
originals and for the copies. But if the throw statement is in place:
A:this(this)
B:this(this)
B:~this
A:~this
object.Exception at test99.d(12): Boom

We see that the destructors for the copies are not called. It can be argued
that this is valid for the B copy, as it's postblit threw.

But for the copy of A the destructor must be called as the postblit was called
and succeeded.


The problem is that the destructors are currently called in the callee but the
postblits in the caller. If an exception is thrown in between those calls, the
destructor can't be called.

A possible solution is to move the destructor to the caller. But in this case
the parameter (the copy) must be passed by invisible reference so that the
destructor actually sees the updated value after the callee returns.

(Note that it might be useful to make an exception for non-PODs without
destructors here. Those shouldn't be affected by this issue and could be
treated like PODs when being passed to a function as an optimization.)

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