Re: jvm wishes and gripes

[Per Bothner <per at bothner dot com>]

Adam Megacz wrote:
>
> Oh yeah, one more thing... why doesn't the Java Language spec allow
> this:
> 
>   class A {
>       A foo() { return null; }
>   }
> 
>   class B extends A {
>       B foo() { return null; }
>   }
> 
> Plenty of other languages (Haskell, ML) 
and C++

> let you do stuff like
> this... the code above can't violate typing rules (even if B.foo()
> returned actual instances of B instead of just null).

They did want to add it, but implementation issues made it awkward to
implement, and they were under get-it-out-the-door pressure.  My
guess is that the problem is the way the return type of a method is
part of its signature, and that name+signature is used for method
matching.  There are lots of other problems in Java that could have
been done better with more time.
-- 
	--Per Bothner
per@bothner.com   http://www.bothner.com/per/