From: Robert Klemme <bob.news@...>
Date: 2005-09-26T18:46:41+09:00
Subject: Re: Overloading

Ben wrote:
> I'm a C++ programmer learning Ruby.  I would like to make a class that
> extracts patterns from a file, and returns an array of values.  I
> have:
>
> class Extracter
>   def initialize(pattern, location)
>     @pattern = pattern
>     @loc = location
>   end
>   def extract(stream)
>     pats = Array.new
>     stream.each_line do |line|
>       if line =~ @pattern then
>         pats << $~[@loc]
>       end
>     end
>     pats
>   end
> end
>
> cppFile = File.new("foo.cpp")
> incEx = Extracter.new(/#include\s*[<"](.*)[>"]/, 1)
> includesArr = incEx.extract(ccpFile)
>
> So far, so good.  If not, let me know what I've done wrong.  Next, I
> want to extend the Extracter class to hold an array of patterns and
> locations, or a Proc parser that will return the interesting value
> (this is for lines that are tougher than regexp).  How do I create a
> constructor that will take different types and create the appropriate
> arrays internally?  The options I see are:
>
> 1) Call .class.to_s on each parameter to match the type:
>         "pattern.class.to_s =~ /Array/ then # I have an array of
> regexp 2) Use a non-trvial data structure to map symbols to types
> 3) Use different functions to fill out my extracter:
>         def add_array
>         def add_parser
>
> What am I missing?  Am I doing this entirely wrong for Ruby?

General stuff about method overloading and C++ like constructs:
http://www.rubygarden.org/ruby?MethodOverloading
http://www.rubygarden.org/ruby?RubyFromCpp

In your case I'd probably do it differently.  Maybe something like this:

def extract(io)
  result = []
  io.each_line do |line|
    dat = yield line and result << dat
  end
  result
end

includes = File.open("foo.cpp") do |io|
  extract io {|line| /#include\s*[<"](.*)[>"]/ =~ line and $1 }
end

Btw, your regexp might be too greedy because you use ".*".  Alternatives
that might work:

/#include\s*[<"](.*?)[>"]/
/#include\s*[<"]([^>"]*)[>"]/

Kind regards

    robert