Thread overview
[Issue 8683] New: bad type resolution for template property functions
Sep 18, 2012
Ellery Newcomer
Oct 05, 2012
Andrej Mitrovic
Oct 05, 2012
Maxim Fomin
Oct 05, 2012
Maxim Fomin
Oct 08, 2012
Ellery Newcomer
September 18, 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8683

           Summary: bad type resolution for template property functions
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: ellery-newcomer@utulsa.edu


--- Comment #0 from Ellery Newcomer <ellery-newcomer@utulsa.edu> 2012-09-17 21:00:30 PDT ---
code:

@property int Foo()() {
    return 1;
}

@property int Goo() {
    return 1;
}

pragma(msg, typeof(Foo));
pragma(msg, typeof(Goo));

void main() {
    import std.stdio;
    writeln(Foo);
    writeln(Goo);
}


should spit out

int
int

does spit out

void
int

when compiled.

prints

1
1

when ran.

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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> 2012-10-04 18:59:29 PDT ---
Maybe typeof(Foo!()) is required here?

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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> 2012-10-05 10:35:47 PDT ---
(In reply to comment #0)
>
<skip>

It may or may not be a bug depending on what spec says and it says little about it. Dlang.org template page says that semantic analysis is done after template instantiation and in your case it is not instantiated. On the one hand, it is obvious that return type does not vary and is always int. On the other hand, dmd is not obligated to do so until full template instantiation.

TDPL p.139-140 says that D uses heterogeneous translation which means that int
Foo()() is not a compiled function like int Goo(). At p.236 it additionally
says that Foo()() is not a type, it's a means to create a type. This means that
asking a typeof from something that is not a type is problematic.

The key point here is whether typeof(Foo) should instantiate type or not for templates like Foo. If it should instantiate, then it should correctly parse return type. If not (and it seems that typeof of templates which cannot be easily instantiated as Foo), than typeof should return some invalid type (like void) or just issue error.

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--- Comment #3 from Maxim Fomin <maxim@maxim-fomin.ru> 2012-10-05 10:37:03 PDT ---
This code demonstrates the issue http://dpaste.dzfl.pl/9f2cc42f

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--- Comment #4 from Ellery Newcomer <ellery-newcomer@utulsa.edu> 2012-10-07 17:51:37 PDT ---
(In reply to comment #1)
> Maybe typeof(Foo!()) is required here?

That does work, but I don't see why


pragma(msg, typeof(Foo));


should fail while


writeln(Foo);


succeeds.

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