• d-bugmail puremagic.com Jul 05 2008
• d-bugmail puremagic.com Jul 06 2008
• d-bugmail puremagic.com Apr 23 2009
• d-bugmail puremagic.com Apr 23 2009

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=2196

           Summary: Link errors with an abstract class's method implementing
                    an interface
           Product: D
           Version: 1.031
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Keywords: link-failure, spec
          Severity: minor
          Priority: P3
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: diggory.hardy gmail.com


The following code generates an error at link time:

interface A
{
    void foo ();
}

abstract class B : A
{
    void foo ();
}

void main() {}


The error:
abstract.o: In function `_TMP0':
abstract.d:(.text+0x4): undefined reference to `_D8abstract1B3fooMFZv'
collect2: ld returned 1 exit status


Marking foo in B as abstract avoids the problem. The documentation isn't at all
clear on whether this should be the case.

Tried with dmd 1.031 and 1.027, and gcc (Debian 4.3.1-2) 4.3.1.


-- 

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=2196





------- Comment #1 from 2korden gmail.com  2008-07-06 05:09 -------
I'm not sure if it is a bug, this is a correct behaviour to me.

In this code:
abstract class B : A {
    void foo ();
}

you define a method foo() and should provide a function body somewhere. Merely
marking class abstract says that you can't instantiate it, but you can any
other class that subclasses from it, unless it is abstract, too. If you mark
you method as abstract it means that there is no body, child class should
provide an implementation.

Interface methods are implicitly abstract.


-- 

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=2196


gide nwawudu.com changed:

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




------- Comment #2 from gide nwawudu.com  2009-04-23 05:12 -------
(In reply to comment #1)
 I'm not sure if it is a bug, this is a correct behaviour to me.
 If you mark your method as abstract it means that there is no body, 
 child class should provide an implementation.


The following compiles correctly, the original code should not link.

interface A {
    void foo ();
}

abstract class B : A
{
    abstract void foo ();
}

void main() {}


-- 

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=2196


diggory.hardy gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |CLOSED




------- Comment #3 from diggory.hardy gmail.com  2009-04-23 08:22 -------
Agreed.

I think what I was unsure on is why the linker wanted the definitions of an
abstract class that wasn't (attempted to be) used. But of course having to
explicitly mark such functions as abstract does make it clear whether or not
the function was intended to be defined in that class.


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