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[janderson]

Dee Girl wrote:
> janderson Wrote:
> 
>> //ie
>> class A
>> {
>>
>> };
>>
>> class B : A
>> {
>>
>> };
>>
>> 	B[] b;
>> 	b ~= new B;
>> 	A[] a = b;
>> 	a ~= new A;
>> //b[1] Is not an A type (not a B type), but is essentially a reinterpret 
>> A -> B.
> 
> Your example compiles but it was so good if it did not. Modifiable arrays should never be covariant! Why did D make the same mistake that Java and Eiffel did? Newer languages should learn from the mistakes of the old languages. This is more than a bit disappointing. Dee Girl


I agree its not particularly good.  Then again, if your using casting 
for anything you should think twice about what your doing.  I think the 
reason for allowing A[] a = b; is polymorphism.  The problem comes when 
you append a new A.  I think the solution would be to make A[] invariant 
or const and enforce it by the compiler.   That way you can't add 
anything to B[] indirectly but can still pass it into functions that 
take invariant A[].