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digitalmars.D.bugs - [Issue 9249] New: Defining opCast disables Upcasting

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9249

           Summary: Defining opCast disables Upcasting
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: blocker
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: puneet coverify.org


--- Comment #0 from Puneet Goel <puneet coverify.org> 2013-01-01 08:20:42 PST
---
This becomes blocking now since opCast is required for implementing toImpl.

test.d(13): Error: template instance opCast!(Foo) does not match template
declaration opCast(T) if (is(T == string))


class Bar {                  // 1
  public T opCast(T)()       // 2
    if(is(T  == string))     // 3
      {                      // 4
        return "Bar";        // 5
      }                      // 6
}                            // 7
                             // 8
class Foo: Bar { }           // 9
                             // 10
void main() {                // 11
  Bar bar = new Foo();       // 12
  Foo foo = cast(Foo) bar;   // 13
}                            // 14

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=9249


Andrej Mitrovic <andrej.mitrovich gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrej.mitrovich gmail.com


--- Comment #1 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2013-01-10
20:40:57 PST ---
What your sample is showing is downcasting, this is upcasting:

class C1
{
    public T opCast(T)()
        if (is(T == string))
    {
        return "C1";
    }
}

class C2 : C1
{
}

void main()
{
    C2 c2;
    C1 c1 = cast(C1)c2;
}

Both fail though.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Puneet Goel <puneet coverify.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Defining opCast disables    |Defining opCast disables
                   |Upcasting                   |downcasting and explicit
                   |                            |upcasting


--- Comment #2 from Puneet Goel <puneet coverify.org> 2013-01-10 20:54:39 PST
---
Yup, my bad. I have updated the summary as per Andrej's comment.

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--- Comment #3 from Andrej Mitrovic <andrej.mitrovich gmail.com> 2013-01-10
20:58:23 PST ---
I've tried a version as old as 2.032 which has the same behavior. It's odd this
wasn't picked up before.

What I think should happen is opCast should be tried first, and if it can't be
instantiated try to do the regular upcast/downcast.

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