[Mono-list] Interface collisions

Quentin DELANCE quentin.delance@insalien.org
Tue, 10 Dec 2002 22:58:09 +0500

Miguel de Icaza wrote:

> Hello,
>>Which is fine except that in the book the output of csc looks even 
>>smarter. The error used is CS 0111 and states that it is not possible to 
>>implement these interface at the same time. It would be nice if mcs 
>>could do the same...
> Please file a `wish list' bug in bugzilla.ximian.com

Well that is not needed after all !

After spending some more time on it, here is another code sample :

$ cat InterfaceCollision.cs
using System;

interface I1 { void F(); }
interface I2 { int F(); }

public class TestClass : I1, I2
    void F() {}
    int F() {}
$ mcs InterfaceCollision.cs
InterfaceCollision.cs(9) error CS0111: Class `TestClass' already defines 
a member called `F' with the same parameter types
Compilation failed: 1 error(s), 0 warnings

This time, I get the expected CS0111 error. The difference is that this 
time, both methods have been implemented in "TestClass" which was not 
the case previously. After rereading Thinking in C#, the behaviour is 
the same for mcs, that's to say :

  + if methods are not implemented -> CS0536 (no checking wether there 
could be conflicts with overloading without explicit implementation by 
prepending the name of the class to the method ie I1.F)
  + if methods are implemented and a conflict exists -> CS0111

Sorry, my first tests were too simple to fully understand the problem. 
As said in the book, these a cases were "implementation and overloading 
get unpleasantly mixed".

> Note that its possible to implement the interface methods if you use
> explicit interface implementation.

Yes, Jonathan also pointed this to me. It is also covered by the book 
and I was not familiar with this syntax !

One must be brave to implement compilers ;)

To sum up, I will only fill a low priority bug for the parser error 
(unexpected key word public in interfaces)

Many thx for the support !