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Newsgroups: comp.lang.java.programmer
From: Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at>
Subject: Re: looping through a list, starting at 1
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Date: 11 Aug 2011 18:03:40 GMT
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Lew <lewbloch@gmail.com> wrote:
> Andreas Leitgeb wrote:
>> Lew wrote:
>>> Andreas Leitgeb wrote:
>>>> Lew wrote:
>>>>> Volker Borchert wrote:
>>>>>> if (l instanceof RandomAccess) {
>>>>> Tests on type like this are an antipattern.
>>>> Are marker-interfaces (which RandomAccess is, iirc) already an
>>>> antipattern, or is there a different way to check for them, [...]
>>> With generics you can use type intersections so that something has to be
>>> both 'List' and 'RandomAccess' (again, say) even to reach the call or the
>>> class or whatever.
>> Interesting stuff! (but still falls a bit short):
>>     public static <T extends List,RandomAccess> T method(T raAcList) {
>>     // public static <T extends List> T method(T anyList) {
> You cannot have two erasure-equivalent methods in the same class, ...

It isn't obvious to me, how these really *need* to be erasure-equivalent.
I mean, obviously they are, but that's just a fact of Java as it is,
not a principial necessity.
If Java had a consistent model of intersection types even outside
of generics, like "List & RandomAccess raList = new ArrayList();",
then the erased type of first method()'s "T" would be just that
intersection type, and the methods would be obviously erasure-
*un*equivalent.
No need to tell me it ain't so.  I know. :-(

> The generics trick is suitable when you want to insist
> that the argument be of the particular type, not when
> you want to bifurcate as you indicated.

But bifurcation was the context of this discussion about
"instanceof"-red flags!

> It seems as though perhaps you are in a situation where you
> want to fork on the type at run-time, ...

Well, not me. See Volker's posting up-thread for the context
in which he suggested use of "instanceof".

Forking on "implementing or not implementing a particular
marker-interface" is an entirely different situation from
asserting a particular interface/type. I'm all with you
that the latter be done at compile-time whenever even
remotely possible.

Now, would you call "instanceof" in the specific context of
bifurcation (with none of the branches just barfing) still
a red flag?