From: Joel Pearson <lists@...>
Date: 2013-01-29T21:19:11+09:00
Subject: Re: Please explain in English

Ryan Davis wrote in post #1094171:
> This modifies the argument coming in. Don't ever call downcase! or other
> mutating methods on an argument or you'll wind up in debugging hell.
> Make a copy instead:
>
> string = string.downcase

Ah, I didn't know that a bang method would also change the argument 
outside of the current scope as well! Dangerous.

irb(main):001:0> a = 'a'
=> "a"
irb(main):002:0> def t1(b)
irb(main):003:1> b.upcase
irb(main):004:1> end
=> nil
irb(main):005:0> def t2(b)
irb(main):006:1> b.upcase!
irb(main):007:1> end
=> nil
irb(main):008:0> t1 a
=> "A"
irb(main):009:0> a
=> "a"
irb(main):010:0> t2 a
=> "A"
irb(main):011:0> a
=> "A"

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