From: Robert Klemme <shortcutter@...>
Date: 2006-10-28T22:25:12+09:00
Subject: Re: What are closures, continuations?

"Une B�vue" <pere.noel@laponie.com.invalid> wrote:
> Justin Collins <collinsj@seattleu.edu> wrote:
>
>> Closures are tricky, but you can think of them as blocks of code, or
>> a way of making code a first-class object. Or as anonymous functions.
>
> could we say they work as anonymous class in java ???

There are some similarities but also restrictions.  For example you can only 
reference final variables from the current environment which means you 
cannot change them.  That in turn is typically possible with closures:

irb(main):001:0> def counter(init=0) lambda {|*x| init += x[0]||1} end
=> nil
irb(main):002:0> c = counter
=> #<Proc:0x003a6254@(irb):1>
irb(main):003:0> c[]
=> 1
irb(main):004:0> c[]
=> 2
irb(main):005:0> c[]
=> 3
irb(main):006:0> c[]
=> 4
irb(main):007:0> c[10]
=> 14

In a way every class is a closure as its instances carry around some state 
they can always access.  But the term "closure" is generally /not/ used for 
this - this is called "encapsulation".

Kind regards

    robert