From: Mike Gold <mike.gold.4433@...>
Date: 2009-02-07T04:34:22+09:00
Subject: Re: eval statement

Jonathan Wills wrote:
> 
> a = 1
> eval('a=2')
> puts a
> 
> This will print out '2', as I want.  However if I remove the first line,
> 
> eval('a=2')
> puts a

The thing to remember is that local variables are always determined at 
parse time.

The contents of 'a=2' is not seen by the parser when the file is read, 
so in the second case the 'a' in 'puts a' is determined to be a method 
call: "call method 'a', then call method puts".

Constants and instance variables are different, as they are determined 
by their naming scheme and therefore behave more as you expected.

irb(main):001:0> eval("@a = 2")
=> 2
irb(main):002:0> @a
=> 2
irb(main):003:0> eval("X = 3")
=> 3
irb(main):004:0> X
=> 3

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