Question

I have a question about Ruby blocks.
For example I have a Ruby Class:

class NewClass
  def initialize
    @a = 1
  end

  def some_method
    puts @a
  end
end

When I do something like that:

NewClass.new do |c|
  c.some_method
end

Everything is good, but is there any possibilities to do that somehow like:

NewClass.new do
  some_method
end

Any ideas?

Answer 1

Your current code will just ignore the block anyway since you don’t yield to it. For what you are trying to do in your first example you need the yield self idiom in initialize.

For why you need a block variable in the first place, think about what the receiver for some_method would be in your second example. Without an explicit receiver it’s the top level main (unless this code is part of some other class of course, where that enclosing class would be self). See Dave Thomas’ blog post Changing self in Ruby (or Yehuda Katz’ post as pointed out by Niklas B. in the comments) for more info on that topic (the comments clear up the “proc invocation” part).

Edit: all that said, this seems to work, but I prefer the yield self version and example 1:

class NewClass
  def initialize
    @a = 1
  end

  def some_method
    puts "Hello: #@a"
  end

  def self.build(&block)
    x = self.new
    x.instance_eval(&block)
    x
  end
end

NewClass.build do
  some_method
end

This allows you to execute the block without a block variable and will return the new instance of the class for assigning to a variable etc.