From: Ryan Davis <ryand-ruby@...>
Date: 2013-01-29T18:24:33+09:00
Subject: Re: Please explain in English


On Jan 28, 2013, at 10:01 , Joel Pearson <lists@ruby-forum.com> wrote:

> def count_words(string)
>  res = {}
>  string.downcase!
>  string.scan( /\w+/ ).uniq.each{ |word| res[word] =
>    string.scan(/\b#{word}\b/).size }
>  res
> end

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