From: Justin Collins <justincollins@...>
Date: 2008-01-10T10:33:02+09:00
Subject: Re: problem with closure/block

levilista@gmail.com wrote:
> ###########################
> y=5
> print "y: " + y.to_s + "\n"
> text_at_the_end = lambda do |y|
>   print y + " text at the end\n"
> end
>
> print "y: " + y.to_s + "\n"
>
>
> def oneparam
>   yield("oneparam")
> end
>
> oneparam(&text_at_the_end)
> print "y: " + y + "\n"
>
>
> ########################
> It gives the following output:
>
> y: 5
> y: 5
> oneparam text at the end
> y: oneparam
>
>
> Is this a bug? Shouldn't "y" be in a local scope in "text_at_the_end"?
> I just downloadad Ruby yesterday:
>
>     Ruby Version 1.8.6
>     Installer Version 186-2
Blocks in Ruby are closures, so they save the context in which they were 
created, but new variables inside the closure are local.

irb(main):001:0> x = 1
=> 1
irb(main):002:0> l = lambda do |y|
irb(main):003:1* puts x
irb(main):004:1> puts y
irb(main):005:1> end
=> #<Proc:0x00002ae970650e58@(irb):2>
irb(main):006:0> l['hello']
1
hello
=> nil
irb(main):007:0> y
NameError: undefined local variable or method `y' for main:Object
        from (irb):7
        from :0
irb(main):008:0> x
=> 1
irb(main):009:0> x += 1
=> 2
irb(main):010:0> l['again']
2
again
=> nil

Take a look here:
http://ruby-doc.org/docs/ProgrammingRuby/html/tut_containers.html#UG

-Justin