[nem-bug] [Nemerle 0000729]: complex use of Co/contravariance for generic interfaces / delegates

[feedback at nemerle.org]

The following issue has been RESOLVED.
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<http://nemerle.org/bugs/view.php?id=729> 
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Reported By:                Tobias
Assigned To:                nazgul
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Project:                    Nemerle
Issue ID:                   729
Category:                   Compiler
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     resolved
Resolution:                 fixed
Fixed in Version:           
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Date Submitted:             08-05-2006 18:25 CEST
Last Modified:              08-06-2006 16:00 CEST
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Summary:                    complex use of Co/contravariance for generic
interfaces / delegates
Description: 
#pragma indent

using System

public interface ICovariantEnumerator [+T] 
{
  MoveNext () : bool;
  Current : T { get; }
}

public interface ICovariantEnumerable [+T] 
{
  GetEnumerator () : ICovariantEnumerator [T];
  SetEnumerator(e : ICovariantEnumerator [T]) : void;
}


[Record] \
public class Enumerator [T] : ICovariantEnumerator [T]
{
  enu : System.Collections.Generic.IEnumerator [T];
  
  public MoveNext () : bool
  {
    enu.MoveNext ();
  }
  
  public Current : T {
    get { enu.Current }
  }
}

public class Enumerable [T] : ICovariantEnumerable [T]
{
  mutable enu : ICovariantEnumerator [T];
  
  public GetEnumerator () : ICovariantEnumerator [T]
  {
    enu;
  }
  public SetEnumerator (e : ICovariantEnumerator [T]) : void
  {
    enu = e;
  }
}

def int_list = Enumerable() : ICovariantEnumerable[int]
def string_list = ["a", "b", "c"]
def object_list = int_list : ICovariantEnumerable[object]
def e_s = Enumerator(string_list.GetEnumerator()) :
ICovariantEnumerator[string]
def e_o = e_s : ICovariantEnumerator[object]
object_list.SetEnumerator(e_o)
foreach(i in int_list) {
	Console.WriteLine(i)
}
_ = Console.ReadLine()



Compiles but you get

TypeLoadException:
Could not load type 'ICovariantEnumerable`1' from assembly 'Test,
Version=0.0.0.0, Culture=neutral, PublicKeyToken=null' because a covariant
or contravariant type parameter was used illegally in the signature for an
argument in method 'SetEnumerator'.

when running
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----------------------------------------------------------------------
 nazgul - 08-06-06 16:00 
----------------------------------------------------------------------
Thanks, I missed the point of "inverting" the set of variance signs (S) in
the implementation. :)

Fixed on trunk (r6487).

Issue History
Date Modified  Username       Field                    Change              
======================================================================
08-05-06 18:25 Tobias         New Issue                                    
08-05-06 18:25 Tobias         File Added: cocontra.patch                    
08-06-06 16:00 nazgul         Status                   new => resolved     
08-06-06 16:00 nazgul         Resolution               open => fixed       
08-06-06 16:00 nazgul         Assigned To               => nazgul          
08-06-06 16:00 nazgul         Note Added: 0001397                          
======================================================================