Re: foreach considered dangerous?

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From: Daniel O'Connell [C# MVP] (onyxkirx_at_--NOSPAM--comcast.net)
Date: 05/06/04 

Date: Thu, 6 May 2004 18:14:15 -0500

"cody" <no_spam_deutronium@gmx.net> wrote in message
news:%23eHSu63MEHA.3312@tk2msftngp13.phx.gbl...
> foreach does implicitly cast every object in the collection to the
> specified
> taget type without warning.
> Without generics this behaviour had the advantage of less typing for us
> since casting was neccessary in nearly every collection. But with generics
> I
> consider this feature of foreach as dangerous. Casting is now almost
> always
> unwanted.
>
> interface IFoo{}
> class Foo:IFoo{}
> class FooBar:IFoo{}
>
> IFoo[] fooarray = {new Foo()} ;
>
> foreach (FooBar in fooarray) // oops InvalidCastException
> {
> }
>
> My proposal is now that foreach should in future emit a compiler warning
> if
> implicit cast would occur.
>
The problem is that, without generics, you don't have a choice. And, sorry
to say it, assuming that everything will be generic is short sighted. You
will have to deal with collections typed as object for a long time to come.
foreach isn't dangerous in itself, its the developers fault if anything
fails, especially consdiering you defined the type and should be aware that
means a cast. If you have a collection that isn't strongly typed and you are
concerned it may hold incorrect data, you should be using for and as.

Having said that, the compiler should catch you if you use a type that an
IEnumerable<T> cannot cast or convert to. Which, frankly, is the desired
behaviour. Just throwing a warning if an implicit cast *may* happen on a
enumerator typed object is silly when the compiler can tell you that your
generic enumerator *cannot* perform the cast you want when the type is
FooBar but can't tell you that your cast on object will.

There is no reason to break existing behavior here, and a warning is
certainly not warranted. An error is when the type you request doesn't match
T of any IEnumerable<T> that is available, but thats a different matter
entirely.

> --
> cody
>
> Freeware Tools, Games and Humour
> http://www.deutronium.de.vu || http://www.deutronium.tk
>
>

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