From: 7stud -- <dolgun@...>
Date: 2007-10-11T22:16:31+09:00
Subject: Re: Why does this use a block

Anonymous wrote:
> So I'm new to Ruby and I'm trying to use OptionParser to parse in some
> command line arguments. 

In ruby, a lot of methods can be called with or without a block.  When a 
method is called with a block, it may do some extra stuff.  I think what 
the other posters are saying is that the initialize() method in 
OptionParser, which is called when you call new(), may be defined to do 
some extra things when it's called with a block.

Here's an example of a method doing some extra things when it's called 
with a block:

class Dog
  def age
    @age
  end

  def age=(num)
    @age = num
  end

  def initialize
    if block_given?
      yield self

      if @age == nil
        puts "You must set the dog's age."
      elsif @age > 20
        puts "Error.  That dog is dead."
      elsif @age < 0
        puts "Error.  That dog isn't born yet."
      end

    end
  end
end



d = Dog.new
d.age = -3
puts "That dog's age is #{d.age}."
d.age = 22
puts "That dog's age is #{d.age}."

d = Dog.new do |dog|
  dog.age = 22
end

--output:--
That dog's age is -3.
That dog's age is 22.
Error.  That dog is dead.
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