http://d.puremagic.com/issues/show_bug.cgi?id=9218

           Summary: [2.061] Correct signature of struct opCmp no longer
                    accepts enum structs
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: rejects-valid
          Severity: regression
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: siegelords_abode@yahoo.com


--- Comment #0 from siegelords_abode@yahoo.com 2012-12-27 10:00:40 PST ---
This code worked fine in 2.060, errors with 2.061 beta 1:

struct A
{
    enum zero = A(); // Error: A() is not an lvalue

    int opCmp(const ref A a) const
    //int opCmp(A a)
    {
        return 1;
    }
}

void main()
{
    A a;
    auto b = a > A.zero;
    assert(typeid(a).xopCmp !is null);
}

Obviously I could use a different signature for opCmp (e.g. the one I commented out) but then the assert below will fail, as only the correct signature of opCmp is accepted. Fixing either this bug or http://d.puremagic.com/issues/show_bug.cgi?id=8561 would be good enough for me.

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Andrej Mitrovic <andrej.mitrovich@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrej.mitrovich@gmail.com


--- Comment #1 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2012-12-27 14:57:01 PST ---
Since it's a struct you can also use:

int opCmp()(auto const ref A a) const

Otherwise I don't think this is a rejects-valid, it's a documentation issue. Struct literals (manifests included) are no longer lvalues in 2.061, this is by design.

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--- Comment #2 from siegelords_abode@yahoo.com 2012-12-27 22:02:13 PST ---
(In reply to comment #1)
> Since it's a struct you can also use:
> 
> int opCmp()(auto const ref A a) const

This fails the assert.

> Otherwise I don't think this is a rejects-valid, it's a documentation issue. Struct literals (manifests included) are no longer lvalues in 2.061, this is by design.

Then this bug highlights what a bad set of design decisions it was to both make struct literals not lvalues AND require the proper opCmp signature to function only for lvalues.

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SomeDude <lovelydear@mailmetrash.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lovelydear@mailmetrash.com


--- Comment #3 from SomeDude <lovelydear@mailmetrash.com> 2012-12-28 04:57:16 PST ---
Tested on DPaste, this code runs successfully with DMD 2.x Git (UDA beta build)
(supposedly updated daily) both in 32 and 64 bits.

http://dpaste.dzfl.pl/fork/54f9a9e5

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
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                 CC|                            |bugzilla@digitalmars.com


--- Comment #4 from Walter Bright <bugzilla@digitalmars.com> 2012-12-28 16:43:35 PST ---
(In reply to comment #3)
> Tested on DPaste, this code runs successfully with DMD 2.x Git (UDA beta build)
> (supposedly updated daily) both in 32 and 64 bits.
> 
> http://dpaste.dzfl.pl/fork/54f9a9e5

I haven't been able to open that link. In general, I think it's better to just paste code examples inline here.

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--- Comment #5 from Walter Bright <bugzilla@digitalmars.com> 2012-12-28 16:51:22 PST ---
Solving the rvalue reference problem, Issue 9238, is the correct way to resolve this. Unfortunately, I think it would be too disruptive to add such a large change with potential side effects in at the last minute, so I'd like to defer this to the next version.

In the meantime, you can workaround by providing an overload:

    int opCmp(const A a) { return 1; }

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bearophile_hugs@eml.cc changed:

           What    |Removed                     |Added
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                 CC|                            |bearophile_hugs@eml.cc


--- Comment #6 from bearophile_hugs@eml.cc 2012-12-28 16:52:49 PST ---
(In reply to comment #4)
> I haven't been able to open that link.


The code:

struct A
{
    enum zero = A(); // Error: A() is not an lvalue

    int opCmp(const ref A a) const
    //int opCmp(A a)
    {
        return 1;
    }
}
void main()
{
    A a;
    auto b = a > A.zero;
    assert(typeid(a).xopCmp !is null);
}


test.d(3): Error: A() is not an lvalue

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--- Comment #7 from siegelords_abode@yahoo.com 2012-12-29 08:05:49 PST ---
I worked around this for now by adding this overload:

int opCmp(const A a) const
{
    return opCmp(a);
}

This seems to work because the compiler prefers the const ref version to the const version.

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--- Comment #8 from SomeDude <lovelydear@mailmetrash.com> 2012-12-29 08:11:17 PST ---
(In reply to comment #4)
> (In reply to comment #3)
> > Tested on DPaste, this code runs successfully with DMD 2.x Git (UDA beta build)
> > (supposedly updated daily) both in 32 and 64 bits.
> > 
> > http://dpaste.dzfl.pl/fork/54f9a9e5
> 
> I haven't been able to open that link. In general, I think it's better to just paste code examples inline here.

It's the code of the original problem description.
I copy it in DPaste because it offers a very convenient way to test it with the
three main D compilers in both 32 and 64 bits without having to install these
compilers on one's own computer. DPaste offers the 2.060 compilers as well as
the latest overnight version of the main branch, so it's quite convenient for
quick testing.

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--- Comment #9 from siegelords_abode@yahoo.com 2012-12-29 09:13:28 PST ---
Ok, that workabout is not quite complete (perhaps this is a different bug now?). While it solves the code in the original comment, this code doesn't work:

struct A
{
    enum A zero = {}; // Note the difference here

    int opCmp(const ref A a) const
    {
        return 1;
    }

    int opCmp(const A a) const
    {
        return opCmp(a);
    }
}

void main()
{
    A a;
    auto b = a >= A.zero; //The error is now here! test.d(21): Error: A() is
not an lvalue
    auto c = a > a;
    assert(typeid(a).xopCmp !is null);
    typeid(a).xopCmp(&a, &a);
}

Why would enum A zero = A(); work but enum A zero = {}; not work? Is it safe
(in terms of inadvertent GC usage) to use A() instead of {}?

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