From: Sam Sungshik Kong <ssk@...>
Date: 2004-10-20T03:04:20+09:00
Subject: Question about closure

Hi, group!

I am trying to understand what exactly a closure is.
I'm kinda familiar with C#.
In C# 2.0 (the next version that's coming out), there's a anonymous
delegate.
People say that it's a closure (See
http://martinfowler.com/bliki/Closures.html).
They even compare it with Ruby codes saying that closure is block.
Is it true?

When I saw the closure example in Ruby, it was not just a block.

Here's a typical example of Ruby closure.

<snip>
def makeCounter
  var = 0
  lambda do
    var +=1
  end
end

c1 = makeCounter
c1.call
c1.call
c1.call

c2 = makeCounter

puts "c1 = #{c1.call}, c2 = #{c2.call}"
</snip>


Here is what the above page(http://martinfowler.com/bliki/Closures.html)
says...

<snip>
Closures have been around for a long time. I ran into them properly for the
first time in Smalltalk where they're called Blocks. Lisp uses them heavily.
They're also present in the Ruby scripting language - and are a major reason
why many rubyists like using Ruby for scripting.

Essentially a closure is a block of code that can be passed as an argument
to a function call.

....

In a language that has Closures, in this case Ruby, I'd write this.

def managers(emps)
 return emps.select {|e| e.isManager}
end
</snip>

This is just a block, right?
Is it also a closure?

I'm confused.
Can somebody enlighten me?


Sam