From: "zslevi@..." <levilista@...>
Date: 2008-01-12T02:24:59+09:00
Subject: Re: problem with closure/block

On Jan 10, 9:13 am, "zsl...@gmail.com" <levili...@gmail.com> wrote:
> "Blocks in Ruby are closures, so they save the context in which they
> were
> created, but new variables inside the closure are local. "
>
> I just expected, that if the head of the closure has x, it will create
> a new local variable with the same name.
>
> On Jan 10, 2:33 am, Justin Collins <justincoll...@ucla.edu> wrote:
>
> > levili...@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

I think it's an advantage in javascript, that you have to mark new
variables with "var", so the scope of a variable is always obvious.