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Re: Polymorphism, genericity, etc.
Maciej Stachowiak wrote:
> I don't buy it. Having "integer_list" inherit from "list" is
> the kind of mistake beginning OO-programmers make (assuming
> here that a "list" is a list of some root "object" type which
> is a supertype of anything).
I think Meyer's example if I remember correct (and which went through a
troublesome period of fashion when C++ lacked templates) is that the
item you are putting in a list inherits from list_member. So if you want
to put dogs in a list you change dog to inherit from list_member. And
then you have the problem of getting the object back out again without
> formal parameters (as opposed to return types) are forbidden by
> most languages
> because they are __not_ type-safe.
In Eiffel they used to be type-safe because global checks were done.
Very ugly in a theoretical sense. I've got a feeling they might have
some other solution now.
> Actually, Java's built-in array types exhibit the covariance
> problem I described above, one of several glaring design flaws
> in the Java language. In other words, it will allow you to pass
> a String where an Object is expected, and throw run-time
> type errors if you then try to assign a non-String to an
> element of the array.
> So much for the benefits of static typing.
Yep, if you're going to do type-safe, you need to do it properly. And
when you do it properly the language can get pretty complicated.
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