Thread overview
[Issue 11382] New: Bad closure variable with scoped destruction
Oct 30, 2013
Kenji Hara
Oct 30, 2013
Kenji Hara
Oct 30, 2013
Maxim Fomin
Oct 30, 2013
Ali Cehreli
October 30, 2013
http://d.puremagic.com/issues/show_bug.cgi?id=11382

           Summary: Bad closure variable with scoped destruction
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: accepts-invalid
          Severity: critical
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: k.hara.pg@gmail.com


--- Comment #0 from Kenji Hara <k.hara.pg@gmail.com> 2013-10-29 21:32:40 PDT ---
In the following code, compiler should reject the function 'foo' by "has scoped destruction, cannot build closure" error.

struct S
{
    ~this() {}
}

auto foo()
{
    S s = S();
    return { s = S(); };
}

void main() {}

It is checked in toir.c FuncDeclaration::buildClosure(), however currently it doesn't work for the variables which are explicitly declared on statement.

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--- Comment #1 from Kenji Hara <k.hara.pg@gmail.com> 2013-10-29 21:33:06 PDT ---
Related discussion: http://forum.dlang.org/thread/wsketyuhrbwiaetfbfww@forum.dlang.org

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |maxim@maxim-fomin.ru


--- Comment #2 from Maxim Fomin <maxim@maxim-fomin.ru> 2013-10-30 05:48:08 PDT ---
I think this may break some code but I am not sure about that.

What is more important is that conclusion in relevant threads was just not to place dtor invocation in the end of function scope because stack struct touched by closure is essentially object residing in the heap, and structs allocated in the heap typically have no dtor call (unless they are wrapped into class or some trick is used). Your proposal to reject code comes from nowhere and it is unnecessary restrictive and does not fit into current practice: allocating structs via new is allowed.

I think right solution is those raised into the thread: just disable dtor invocation in the end of the function scope. Probably some temporal warning will be needed.

In any case, except of struct touched by closure scenario, there are additional cases which should be fixed: nested function and nested structs.

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Ali Cehreli <acehreli@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |acehreli@yahoo.com


--- Comment #3 from Ali Cehreli <acehreli@yahoo.com> 2013-10-30 14:16:37 PDT ---
The rest of the discussion:

  http://forum.dlang.org/post/l4osr0$2f3q$1@digitalmars.com

Ali

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