From: John Sikora <john.sikora@...>
Date: 2010-10-07T11:19:13+09:00
Subject: Re: setting local variables in a binding

Tony Arcieri wrote:
> Note that "binding" is the default argument of eval if you don't specify
> one, so capturing binding as a variable and passing it explicitly is
> redundant.

You are correct but the problem 'persists'. The following irb session in 
1.9.2 shows the same thing without the binding:

irb(main):001:0> eval("x=5")
=> 5
irb(main):002:0> x
NameError: undefined local variable or method `x' for main:Object
        from (irb):2
        from C:/Ruby192/bin/irb:12:in `<main>'
irb(main):003:0> x=4
=> 4
irb(main):004:0> eval("x=5")
=> 5
irb(main):005:0> x
=> 5
irb(main):006:0>


In order for this to work, the x needs to be @x per the following irb 
session (again 1.9.2):

irb(main):001:0> eval("@x=5")
=> 5
irb(main):002:0> @x
=> 5
irb(main):003:0>

The behavior seen in the first irb session was the same in 1.8.6, 1.9.1, 
and 1.9.2 when run standalone. However, it works in irb for 1.8.6 (x w/o 
the @).

I have sometimes seen 'local' or 'unassociated' instance variables (not 
sure if my terminology is correct) in example programs and I have 
wondered why they are used. I guess this is one reason although most 
people don't like to use eval.

I use eval in personal scripts since it is so convenient. Had to go back 
and look at some code to remind myself how I got around the behavior 
seen in the first irb session. I don't remember if I read about using 
the local instance variable or just played around with it until I got it 
to work.

js
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