https://issues.dlang.org/show_bug.cgi?id=19179

Manu <turkeyman@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |C++, industry, wrong-code

--- Comment #1 from Manu <turkeyman@gmail.com> ---
Oops, my cut&paste removed the `extern(C++):` at the top of the D source.
Those 2 test functions should be extern(C++)!

--

https://issues.dlang.org/show_bug.cgi?id=19179

Mike Franklin <slavo5150@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |slavo5150@yahoo.com
           See Also|                            |https://issues.dlang.org/sh
                   |                            |ow_bug.cgi?id=5570

--

https://issues.dlang.org/show_bug.cgi?id=19179

Jack <look.at.me.pee.please@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |look.at.me.pee.please@gmail
                   |                            |.com

--- Comment #2 from Jack <look.at.me.pee.please@gmail.com> ---

Can't reproduce with your example, I've come across something similar in the past though. If you swap your struct with this one:


struct SmallStruct {
        int x, y;

        SmallStruct()
        {
                x = 10;
                y = 20;
        }
};

static_assert(!std::is_pod<SmallStruct>::value, ""); // not a POD, your other
struct is a POD though


the D version will be POD though. But since you can't have a default constructor in D, you have to use another method to make it not POD. That is give it a destructor "~this()" or a copy constructor "this(this)".

Windows treats structs that aren't POD differently if they are less than 8 bytes. That's the root of the problem.

A solution would be to add an attribute "@NotPOD struct blah { }" or something, rather than having to put an empty constructor. Not exactly something that is easy to notify the user of if this inconsistency exists.

--

https://issues.dlang.org/show_bug.cgi?id=19179

--- Comment #3 from Manu <turkeyman@gmail.com> ---
I think what should probably happen here, is that while the type in D is POD, the counterpart in C++ is not POD because default initialisation generates a constructor.

Perhaps the proper solution is to make the D struct emit a default constructor (this just assign's init), and also force the type to use the non-POD ABI? This way semantics will match C++, and if the C++ class externs to the default constructor; it will link as they expect.

--

https://issues.dlang.org/show_bug.cgi?id=19179

Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |backend
                 CC|                            |bugzilla@digitalmars.com

--

https://issues.dlang.org/show_bug.cgi?id=19179

Dlang Bot <dlang-bot@dlang.rocks> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull

--- Comment #4 from Dlang Bot <dlang-bot@dlang.rocks> ---
@WalterBright created dlang/dmd pull request #11698 "fix Issue 19179 - extern(C++) small-struct by-val uses wrong ABI" fixing this issue:

- fix Issue 19179 - extern(C++) small-struct by-val uses wrong ABI

https://github.com/dlang/dmd/pull/11698

--

https://issues.dlang.org/show_bug.cgi?id=19179

Dlang Bot <dlang-bot@dlang.rocks> changed:

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

--- Comment #5 from Dlang Bot <dlang-bot@dlang.rocks> ---
dlang/dmd pull request #11698 "fix Issue 19179 - extern(C++) small-struct by-val uses wrong ABI" was merged into master:

- b6f570491c6972aa865d1f2e6e19535127a58a06 by Walter Bright:
  fix Issue 19179 - extern(C++) small-struct by-val uses wrong ABI

https://github.com/dlang/dmd/pull/11698

--

https://issues.dlang.org/show_bug.cgi?id=19179

jacob <look.at.me.pee.please@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|FIXED                       |---

--- Comment #6 from jacob <look.at.me.pee.please@gmail.com> ---
Please read the comments. If you had, you'd have known that the test Manu gave didn't contain the bug.

--

https://issues.dlang.org/show_bug.cgi?id=19179

Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |RESOLVED
         Resolution|---                         |INVALID

--- Comment #7 from Walter Bright <bugzilla@digitalmars.com> ---
Default initialization in C++ doesn't make it non-POD. And I added the `extern(C++)` to the test cases that Manu had omitted.

Is the actual problem trying to create a non-POD struct in D that is compatible with a non-POD struct in C++?

As to how to make a POD in D without a default constructor, just add a trivial postblit:

    this(this) { }

and it will be not POD.

If there's still a problem, please file a new report explaining what that is rather than reopening this as a different issue.

--