[Issue 3180] New: Need delegate covariance and contravariance

[Issue 3180] Covariance of delegates/function pointers

Jun 09, 2011

yebblies

Jun 13, 2011

Aug 18, 2011

Sep 02, 2011

Sep 06, 2011

Sep 06, 2011

Sep 06, 2011

Sep 06, 2011

Sep 17, 2011

Sep 17, 2011

Sep 18, 2011

July 15, 2009

[Issue 3180] New: Need delegate covariance and contravariance

Posted by rayerd.wiz@gmail.com

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rayerd.wiz@gmail.com

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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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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. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------

http://d.puremagic.com/issues/show_bug.cgi?id=3180 --- 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. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------

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. *** -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------

http://d.puremagic.com/issues/show_bug.cgi?id=3180 --- 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. *** -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------

http://d.puremagic.com/issues/show_bug.cgi?id=3180 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. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------

http://d.puremagic.com/issues/show_bug.cgi?id=3180 yebblies <yebblies@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |zan77137@nifty.com --- Comment #7 from yebblies <yebblies@gmail.com> 2011-06-13 12:16:14 PDT --- *** Issue 4218 has been marked as a duplicate of this issue. *** -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------

http://d.puremagic.com/issues/show_bug.cgi?id=3180 yebblies <yebblies@gmail.com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |bugzilla@kyllingen.net --- Comment #8 from yebblies <yebblies@gmail.com> 2011-08-19 01:50:28 EST --- *** Issue 6524 has been marked as a duplicate of this issue. *** -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------

http://d.puremagic.com/issues/show_bug.cgi?id=3180 Walter Bright <bugzilla@digitalmars.com> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED CC| |bugzilla@digitalmars.com Resolution| |FIXED --- Comment #9 from Walter Bright <bugzilla@digitalmars.com> 2011-09-02 02:38:23 PDT --- Partial fix: https://github.com/D-Programming-Language/dmd/commit/306df8eaa6f8a987f76f401a1e03d8edf1f1e2ae -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------

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