[nem-en] casting operators

[Ivan Lakhturov]

Hello devel-en,

  there is a bunch of problems with casting operators

  let's start from this kind of problem:
  cast operators are not visible from outside of nemerle-assembly

  code for playing with:

  nemerle-code:

namespace BothOverloadsDefined
{
  public class A
  {
    public override ToString() : string
    {
      "instance of A"
    }
  }
   
  public class B : A
  {
    //public static @:(_ : A) : B
    //{
          //System.Console.WriteLine("called A : B implicit cast");
      //B()
    //}
  //
    public static @:>(_ : A) : B
    {
          System.Console.WriteLine("called A :> B explicit cast");
      B()
    }
  
    public static @:>(_ : int) : B
    {
          System.Console.WriteLine("called int :> B explicit cast");
      B()
    }

    public override ToString() : string
    {
      "instance of A"
    }

    static Main() : void
    {
      //def a = A();
      //def b : B = a :> B;
    }
  }
}


  csharp code (add reference on nemerle-code that is above):

using System;
using BothOverloadsDefined;

namespace ConsumeBothOverloadsInCSharp
{
    class Ancestor
    {
    }

    class ClassDefinesImplicitCast : Ancestor
    {
        public static implicit operator ClassDefinesImplicitCast(int n)
        {
            return new ClassDefinesImplicitCast();
        }
    }

    //class ClassDefinesExplicitCast : Ancestor
    //{
    //    public static explicit operator ClassDefinesExplicitCast(Ancestor ancestor)
    //    {
    //        return new ClassDefinesExplicitCast();
    //    }
    //}

    class Some
    {
        static void Main()
        {
            A a = new A();
            Console.WriteLine(a);
            B b = new B();
            Console.WriteLine(b);

            //b = a; // error CS0266: Cannot implicitly convert type 'BothOverloadsDefined.A' to 'BothOverloadsDefined.B'. An explicit conversion exists (are you missing a cast?)
            try
            {
                // System.InvalidCastException: Unable to cast object of type 'BothOverloadsDefined.A' to type 'BothOverloadsDefined.B'.
                b = (B)a;
            }
            catch (Exception e)
            {
                Console.WriteLine(e);
            }

            Console.ReadKey();
        }
    }
}
  

  compile and see under reflector what is there:
  nemerle-defined casts are just public static methods, they don't
  have special attribute to show the external assemblies that they are
  actually casts

  nemerle-decompiled code:
  c#:
public static B op_Explicit(int _N_u1151);
  il:
.method public hidebysig static BothOverloadsDefined.B op_Explicit(int32 _N_u1151) cil managed
 
  c#-decompiled code:
  c#:
public static implicit operator ClassDefinesImplicitCast(int n);
  il:
.method public hidebysig specialname static ConsumeBothOverloadsInCSharp.ClassDefinesImplicitCast op_Implicit(int32 n) cil managed


  there is no "specialname" attribute on nemerle-defined casts, so
  they're invisible from the c# consumer assembly

regards, phantom