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Re: bindings and assignments
At 7:58 PM +0300 8/14/03, vkarvone@mappi.helsinki.fi wrote:
>Quoting Matt Hellige <matt@immute.net>:
>> ["David B. Tucker" <dbtucker@cs.brown.edu>]
>> > > I imagine, though I don't have statistical evidence, that the
>> > > requirement of declaring local variables to be final in order to
>> > > reference them within anonymous inner classes (closures) is almost
>> > > entirely unknown and unused in practice.
>
>I use it regularly in Java.
>
>> > Out of curiosity, does anyone know why Java only allows final
>> > variables to be referenced from within anonymous classes?
>[...]
>> This may be getting off-topic, but hey, you asked for it! Anyway, in
>> my opinion this is one of the largest warts on Java...
>
>As everyone seems to be bashing Java for making this restriction, I'd like
>to point out that languages such as Ocaml (ML style languages) have
>similar (not exactly the same) limitation. In Ocaml, all bindings are
>immutable, but arrays and record fields, for example, are/can be declared
>mutable, which makes Ocaml an imperative language. It doesn't really
>surprise me that people familiar with Ocaml aren't bitching about this
>limitation.
>
>One may argue that Ocaml aims to be (more) functional (than Java), but I
>think that it is red herring, because if one thinks that the feature would
>be useful in Java (making some imperative programs simpler), it should
>basically be useful in Ocaml for the same reasons.
>
>As far as I understand it, designing/implementing automatic boxing to
>allow assignment to captured bindings isn't very involved (maybe a days
>worth of design to implement in a well designed compiler) and allowing it
>in a language (designed to be compiled for high performance) would mean that
>only programs that use the feature (perform assignments to bindings in a
>closure) would pay for the extra boxing, because the boxing needs to be
>performed only when an assignment to a lexically bound variable are found.
>
Here's the distinction:
- People don't bash OCaml because the immutability of bindings
is expected from the design (and design goals) of the language.
- People do bash Java because it's a language built around side-
effects, and adding a seemingly arbitrary restriction requiring
that some things be 'final' in a few places is perceived as
either a design error or just plain laziness.