From: Ruby Quiz <james@...>
Date: 2006-11-25T08:21:24+09:00
Subject: [QUIZ] DictionaryMatcher (#103)

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by Ken Bloom

From time to time someone asks on ruby-talk how they can write a regexp of the
form:

	/alligator|crocodile|bear|dinosaur|...|seven-thousandth-word/

It's not hard to write such a regexp, but Ruby has in internal limit on how big
the regular expression can be, so users find they can't do this matching
function easily.

Implement a class DictionaryMatcher that determines whether any of the strings
added to it are substrings of a string S. This should function as almost a
drop-in replacement for a Regexp, therefore your implementation should support
the following operations:

	# creates a new empty matcher
	dm=DictionaryMatcher.new
	
	# adds strings to the matcher
	dm << "string"
	dm << "Ruby"
	
	# determines whether a given word was one of those added to the matcher
	dm.include?("Ruby")                 # => true
	dm.include?("missing")              # => false
	dm.include?("stringing you along")  # => false
	
	# Regexp-like substing search
	dm =~ "long string"            # => 5
	dm =~ "rub you the wrong way"  # => nil
	
	# will automatically work as a result of implementing
	# DictionaryMatcher#=~ (see String#=~)
	"long string" =~ dm  # => true
	
	# implement the rest of the interface implemented by Regexps (well, almost)
	class DictionaryMatcher
	  alias_method :===, :=~
	  alias_method :match, :=~
	end

If you can add additional features, like a case insensitivity option when
creating a new DictionaryMatcher this is also very useful.