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digitalmars.D.bugs - [Issue 8221] New: typeof(null) rejected as return type for covariant overrides

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8221

           Summary: typeof(null) rejected as return type for covariant
                    overrides
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: timon.gehr gmx.ch



DMD 2.059:

class A{
    A foo(){return this;}
}
class B: A{
    override typeof(null) foo(){return null;} // error
}

The code should compile.

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Jun 11 2012
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=8221


Kenji Hara <k.hara.pg gmail.com> changed:

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



https://github.com/D-Programming-Language/dmd/pull/1001

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Jun 11 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

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



22:50:28 PDT ---
Why should this compile? What is the compelling reason?

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Jun 13 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement


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prev sibling next sibling parent d-bugmail puremagic.com writes:
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 Why should this compile? What is the compelling reason?


typeof(null) is a subtype of array/class/pointer types. By return type
covariance rule, B.foo should be able to override A.foo.

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00:39:47 PDT ---


 typeof(null) is a subtype of array/class/pointer types. By return type
 covariance rule, B.foo should be able to override A.foo.


Since A is not a base class of null, I do not think this is valid. foo could
return B, and that will work, because A is a base class of B.

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Jun 14 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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 typeof(null) is a subtype of array/class/pointer types. By return type
 covariance rule, B.foo should be able to override A.foo.


 
 Since A is not a base class of null, I do not think this is valid. foo could
 return B, and that will work, because A is a base class of B.


No. Indeed A is not a base class of null _liteal_, but A is a base _type_ of
typeof(null).
Current dmd compiles following tests:

static assert(is(typeof(null) : int[]));  // int[]  is a base type of
typeof(null)
static assert(is(typeof(null) : Object)); // Object is a base type of
typeof(null)
static assert(is(typeof(null) : int*));   // int*   is a base type of
typeof(null)

I have implemented typeof(null) as like Scala's Nothing type, so this is
expected result.

In other words, typeof(null) is the most derived class type from all of class
types. So dmd should compile the original code.

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Jun 14 2012
prev sibling next sibling parent d-bugmail puremagic.com writes:
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Commits pushed to master at https://github.com/D-Programming-Language/dmd

https://github.com/D-Programming-Language/dmd/commit/bc55af9d3d38fd18f3a2c1f323cd1a4f49dbd673
fix Issue 8221 - typeof(null) rejected as return type for covariant overrides

https://github.com/D-Programming-Language/dmd/commit/ad7637f3d3c2cdf98ff7de8d715315e8557ee223


Issue 8221 - typeof(null) rejected as return type for covariant overrides

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Jun 22 2012
prev sibling parent d-bugmail puremagic.com writes:
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Walter Bright <bugzilla digitalmars.com> changed:

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


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