http://d.puremagic.com/issues/show_bug.cgi?id=3113

           Summary: final overriding
           Product: D
           Version: 2.030
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: tim.matthews7@gmail.com


This code compiles:

module test;

enum A
{
    a = 0
}

enum B
{
    b = 1
}

class BaseClass
{
    final A getEnum()
    {
        return A.a;
    }
}

class DerivedClass : BaseClass
{
    B getEnum()
    {
        return B.b;
    }
}



void main()
{
    auto der = new DerivedClass();
    der.getEnum();
}

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yebblies <yebblies@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |yebblies@gmail.com
         Resolution|                            |INVALID


--- Comment #1 from yebblies <yebblies@gmail.com> 2011-06-16 04:23:17 PDT ---
B getEnum()
is not overriding
final A getEnum()

It's simply creating a new function.

Yet another reason the override attribute should be compulsory.

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klickverbot <code@klickverbot.at> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
                 CC|                            |code@klickverbot.at
         Resolution|INVALID                     |


--- Comment #2 from klickverbot <code@klickverbot.at> 2011-06-16 05:11:37 PDT ---
Reopening this, as the compiler doesn't even error out with the »-w« switch – the »override compulsory« check seems to be broken in the presence of »final«.

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--- Comment #3 from yebblies <yebblies@gmail.com> 2011-06-16 05:18:11 PDT ---
(In reply to comment #2)
> Reopening this, as the compiler doesn't even error out with the »-w« switch – the »override compulsory« check seems to be broken in the presence of »final«.

Where should the override attribute be required?  There is no overriding happening anywhere in the example.

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--- Comment #4 from klickverbot <code@klickverbot.at> 2011-06-16 05:23:12 PDT ---
R(In reply to comment #3)
> (In reply to comment #2)
> > Reopening this, as the compiler doesn't even error out with the »-w« switch – the »override compulsory« check seems to be broken in the presence of »final«.
> 
> Where should the override attribute be required?  There is no overriding happening anywhere in the example.

Remove the »final« attribute and compile the example with -w, and you'll see.

Besides, since when would it be allowed to have two public methods with the same signature?

--- Comment #5 from klickverbot <code@klickverbot.at> 2011-06-16 05:23:13 PDT ---
R(In reply to comment #3)
> (In reply to comment #2)
> > Reopening this, as the compiler doesn't even error out with the »-w« switch – the »override compulsory« check seems to be broken in the presence of »final«.
> 
> Where should the override attribute be required?  There is no overriding happening anywhere in the example.

Remove the »final« attribute and compile the example with -w, and you'll see.

Besides, since when would it be allowed to have two public methods with the same signature?

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--- Comment #4 from klickverbot <code@klickverbot.at> 2011-06-16 05:23:12 PDT ---
R(In reply to comment #3)
> (In reply to comment #2)
> > Reopening this, as the compiler doesn't even error out with the »-w« switch – the »override compulsory« check seems to be broken in the presence of »final«.
> 
> Where should the override attribute be required?  There is no overriding happening anywhere in the example.

Remove the »final« attribute and compile the example with -w, and you'll see.

Besides, since when would it be allowed to have two public methods with the same signature?

--- Comment #5 from klickverbot <code@klickverbot.at> 2011-06-16 05:23:13 PDT ---
R(In reply to comment #3)
> (In reply to comment #2)
> > Reopening this, as the compiler doesn't even error out with the »-w« switch – the »override compulsory« check seems to be broken in the presence of »final«.
> 
> Where should the override attribute be required?  There is no overriding happening anywhere in the example.

Remove the »final« attribute and compile the example with -w, and you'll see.

Besides, since when would it be allowed to have two public methods with the same signature?

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bearophile_hugs@eml.cc changed:

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


--- Comment #6 from bearophile_hugs@eml.cc 2011-06-16 05:25:54 PDT ---
Even if D is working according to specs, I think this is bug-prone enough to deserve some warning or even an error.

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--- Comment #7 from yebblies <yebblies@gmail.com> 2011-06-16 06:48:41 PDT ---
(In reply to comment #5)
> 
> Remove the »final« attribute and compile the example with -w, and you'll see.
> 

I get an error when compiling without the final attribute, -w or not.

testx.d(21): Error: function testx.DerivedClass.getEnum of type B() overrides
but is not covariant with testx.BaseClass.getEnum of type A()

> Besides, since when would it be allowed to have two public methods with the same signature?

Yes, overloading on return type is disabled for functions in the same scope,
but the rules are a little less strict for deriving classes...
Looking at the spec, it seems to be explicitly disallowed for functions that
would otherwise be virtual.
It can be very useful with template functions, as they need to be redefined in
each class, and is allowed for static functions.

I might be misunderstanding, please post a test case that shows what you mean.

(In reply to comment #6)
> Even if D is working according to specs, I think this is bug-prone enough to deserve some warning or even an error.

I think it would be much clearer if override was mandatory, and I'm fairly sure there's already a report for that.  If there's something else you'd like, please, write it up.  A test case that compiles does not constitute an enhancement request without additional information. (unless it's very, very obvious)

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Steven Schveighoffer <schveiguy@yahoo.com> changed:

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


--- Comment #8 from Steven Schveighoffer <schveiguy@yahoo.com> 2011-06-16 07:54:25 PDT ---
I think it is a bug.  If the case was that a final function could be masked by a derived class, then this should compile:

module test;

enum A
{
    a = 0,
    b = 1
}

class BaseClass
{
    final A getEnum()
    {
        return A.a;
    }
}

class DerivedClass : BaseClass
{
    A getEnum()
    {
        return A.b;
    }
}

But I get the error:
bug3113.d(19): Error: function test.DerivedClass.getEnum cannot override final
function test.BaseClass.getEnum

This occurs even when I mark DerivedClass' function as final.

I was about to mark this as invalid, citing this as a better example, but since the compiler complains about masking in this case, I don't see why the original case is allowed.  I believe this kind of thing is allowed in C++.

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--- Comment #9 from klickverbot <code@klickverbot.at> 2011-06-16 08:06:26 PDT ---
(In reply to comment #8)
> This occurs even when I mark DerivedClass' function as final.

I think it is quite clear that the example you gave shouldn't compile, as the spec has: »Functions marked as final may not be overridden in a derived class, unless they are also private.«

The question now is whether the same behavior should also apply to the example from above. I'm strongly in favor of that, because otherwise, there can be situation where the following two pieces of code don't refer to the same »bar()«, which is completely contrary to how classes usually work in D:

---
auto foo = new Derived();
foo.bar();
---

---
Base foo = new Derived();
foo.bar();
---

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