From: Shawn Anderson <shawn42@...>
Date: 2008-09-20T05:00:33+09:00
Subject: Re: Confused regarding text example

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class WordIndex
 def initialize
   @index = {}
 end
def add_to_index(obj, *phrases)
 phrases.each do |phrase|
   phrase.scan(/\w[\w']+/) do |word| # extract each word
   word.downcase!
   @index[word] = [] if @index[word].nil?
   @index[word].push(obj)
   end
 end
end
def lookup(word)
 @index[word.downcase]
end
end

phrases contains the phases/patterns to look for.  |phrase| is replaced
by each of the phrases to check for.

the *phrases in the method signature says that it takes a variable number of
arguments, you use those as an array of values.

phrases.each do |phrase|
 # code
end
this piece of code defines a block aka closer that takes one argument.  the
each method on array will call this block for every item in the array as the
argument to this block

After that, I become a bit ocnfused.  I know they are looking for the
phrase in each of the words (.\w\w']+/) but how does that work?

/\w[\w']+/ is a shorthand for writing Regexp.new("/\w[\w']+/")
the scan method on a string will return an array of all the matches of that
regexp:
http://ruby-doc.org/core/classes/String.html#M000827


How is each string broken down into "words"?  w

hy is that done anyway (why not just find the pattern and move on?).

The code appears to be adding obj to a hash based on the downcased version
of each word in each phrase.

Also, what is obj exactly (other than an object)?  How is it being
formed so it can be pushed into the stack?

obj is just passed in, it could be anything, it could be the filename that
these words were pulled from.. or whatever you would want to retrieve based
on the words in the phrases associated with it.

Finally, what does index[word] represent?  I am guessing a hash...
See above, you are right!
@index = {}
is shorthand for @index = Hash.new
the same way @foo = [] is shorthand for @foo = Array.new

Hope this helps. If I have made anything unclear please feel free to email
me.

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