Re: Generics Question
- From: Barry Kelly <barry.j.kelly@xxxxxxxxx>
- Date: Fri, 30 Nov 2007 23:46:37 +0000
Scott M. wrote:
I do get your point and I haven't misunderstood anyting (you or the author
of the book I'm reading). You've misunderstood what I'm asking.
Scott, I think I understand what you've misunderstood. I think you
somehow got the idea, once upon a time, that generics enable a certain
class of solutions, where such solutions are semantic in nature (e.g.
write a class that can "maintain a list of stuff", etc.). Now, you've
stumbled across interfaces, and it's dawned on you that you can use
interfaces to do the same semantic thing ("maintain a list of stuff" so
long as "stuff" implements the interface) and you're seeing a semantic
equivalence here.
The thing is, the feature that generics brings to the table, isn't this
capability to implement certain semantics (and thus being equivalent or
a subset of interfaces); it's rather that it enables such semantics *in*
*a* *statically-typed* *way* - and this is the very feature that
interfaces / polymorphism *doesn't* provide. They only work with dynamic
typing.
The fact is that (per my first reply to you) I *can* pass a parameter to my
type that (mechanically) acts as <T> would in a parameterized type.
A parameterized type is a type constructor. By passing it type
arguments, you're creating what effectively is a *new* type, statically
checked at compile time. You *cannot* create such a new type by passing
an interface reference to a constructor.
You know the features that generics bring to the table, but you're
thinking in terms of end results, i.e. observable program actions, and
you can see that interfaces (or ever System.Object) can do the same
thing. But the trouble is, that isn't what generics are about - they
aren't about enabling new kinds of end results, to the exclusion of
other possible implementations. They're all about static typing. Plain
and simple.
-- Barry
--
http://barrkel.blogspot.com/
.
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