Re: Covariant Return Types

>>  override merge(parent, TextElement left, TextElement right) = ...
>>    
>>
>
>I don't think this works in general, when =merge= is overloaded already. 
>
This is not specific to this proposal. Currently, when implementing a 
method which has synonyms (other methods of the same name), you 
sometimes need to disambiguate which one you mean to implement. There 
are ways to do that (adding patterns, and the additional types between 
brackets).

>>(BTW, this example is not covariant so it's unsafe. First fromString 
>>says: I can return you anything you want (if I return!). Then the 
>>implementation does not return anything the client wants, it returns an A.)
>>    
>>
>
>You always catch these. :) 
>
I must have a type-checker built-in or something ;-)

>Try: 
>
>    public A fromString(String s) { throw new Error(); }
>           A fromString("a") = new A();
>           B fromString("b") = new B();
>  
>
Correct, that's covariant.

>But, I think we all agree that this is not something worth allowing.
>  
>
OK.

Daniel



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