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digitalmars.D.bugs - [Issue 3180] New: Need delegate covariance and contravariance

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3180

           Summary: Need delegate covariance and contravariance
           Product: D
           Version: unspecified
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Keywords: spec
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: rayerd.wiz gmail.com


import std.stdio;

class A {}
class B : A {}

class X
{
    A foo() { return new A; }
}
class Y : X
{
    B foo() { return new B; }
}

class V
{
    void foo(B){}
}

void main()
{
    // Class Covariance (supported already)
    {
        X x = new X;
        Y y = new Y;
        A r = x.foo();
        A s = y.foo();
        B t = y.foo();
        writeln(r); // A
        writeln(s); // B
        writeln(t); // B
    }
    // Delegate Covariance
    {
        A delegate() f = delegate A() { return new A; }; // Of course, OK.
        writeln(f()); // A

        //A delegate() g = delegate B() { return new B; }; // Need support the
covariance
        //writeln(g()); // This should be B.
    }


    // Delegate Contravariance
    {
        V v = new V;
        void delegate(B) g = &v.foo; // Of course, OK.
        //void delegate(A) f = &v.foo; // Need suport the contravariance.
    }
}

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3180


Steven Schveighoffer <schveiguy yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |schveiguy yahoo.com
           Severity|normal                      |enhancement




--- Comment #1 from Steven Schveighoffer <schveiguy yahoo.com>  2009-07-15
18:13:10 PDT ---
Your contravariance example is not valid, you cannot call foo(B) with an A.

It should be:

class V
{
  void foo(A);
}


...

V v = new v;
void delegate(B) g = &v.foo; // contravariance

Also this is somewhat of a duplicate of bug 3075.  Although you do bring up
covariance for delegates, which should be implemented at the same time as
contravariance.

Sadly, Walter has decided the prior bug is an invalid enhancement request, so
most likely nothing will come of this request either.

I think the only possible way this may be included is if someone implements it
and submits it as a patch to dmd.

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--- Comment #2 from Haruki Shigemori <rayerd.wiz gmail.com>  2009-07-17
16:55:58 PDT ---
(In reply to comment #1)

 Your contravariance example is not valid, you cannot call foo(B) with an A.
 
 It should be:
 
 class V
 {
   void foo(A);
 }
 
 
 ...
 
 V v = new v;
 void delegate(B) g = &v.foo; // contravariance



Sorry, it is my mistake.


 Also this is somewhat of a duplicate of bug 3075.  Although you do bring up
 covariance for delegates, which should be implemented at the same time as
 contravariance.
 
 Sadly, Walter has decided the prior bug is an invalid enhancement request, so
 most likely nothing will come of this request either.



OMG. It is so sad. There are both in C#.


 I think the only possible way this may be included is if someone implements it
 and submits it as a patch to dmd.



I am trying to make some dmd patchs, but it is difficult yet.

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Jul 17 2009
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3180


Steven Schveighoffer <schveiguy yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dsimcha yahoo.com


--- Comment #3 from Steven Schveighoffer <schveiguy yahoo.com> 2011-03-16
10:08:31 PDT ---
*** Issue 5742 has been marked as a duplicate of this issue. ***

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Mar 16 2011
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=3180


yebblies <yebblies gmail.com> changed:

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


--- Comment #4 from yebblies <yebblies gmail.com> 2011-06-08 22:48:20 PDT ---
*** Issue 3833 has been marked as a duplicate of this issue. ***

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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--- Comment #5 from yebblies <yebblies gmail.com> 2011-06-08 22:48:58 PDT ---
*** Issue 4000 has been marked as a duplicate of this issue. ***

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prev sibling parent d-bugmail puremagic.com writes:
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yebblies <yebblies gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|spec                        |patch, rejects-valid
                 CC|                            |yebblies gmail.com
            Summary|Need delegate covariance    |Covariance of
                   |and contravariance          |delegates/function pointers
           Severity|enhancement                 |normal


--- Comment #6 from yebblies <yebblies gmail.com> 2011-06-08 22:54:07 PDT ---
The enhancement portion of the original report is a dupe of Issue 3075, which
has been marked INVALID by Walter.

In the comments he states that delegate covariance is supposed to work, so that
part of the report is definitely a bug.

https://github.com/D-Programming-Language/dmd/pull/96 
should fix this report for function pointers.

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