From: gga <GGarramuno@...>
Date: 2007-01-19T23:00:07+09:00
Subject: Re: local variable assertion


dflanagan@gmail.com ha escrito:

> I've started studying Ruby, and while I like it, one thing that bothers
> me is that there is not a way to explicitly declare a variable in order
> to say "I want a variable local to this scope: I don't want to reuse
> some variable by the same name in a containing scope."  In particular,
> the fact that giving a block parameter the same name as an existing
> variable can overwrite that variable troubles me.
>
> Now I haven't written enough Ruby code to know whether this is really a
> problem in practice or if it is just a theoretical concern.

I think it is more theoretical, as that would indicate you are really
writing VERY long functions.
Remember that in Ruby, global variables are $, instance variables are @
and class variables are @@, so there's a very rare chance of conflict.

That being said, your code can be done simpler, like:

def let(*syms, &block)
   raise "No block provided for undefined?" unless block_given?

  syms.each do |sym|
        value = eval("defined? #{sym.to_s}", block)
        next if !value
        raise NameError.new("#{sym} is already a #{value}")
   end

   yield
end


# block check
let( :x ) {  x = 20 }

begin
  let( :x ) {   p 'never run' }
rescue
end

# Forgot block...
let( :x )