Question

I’m trying to understand yield in Ruby. In the self.save method of the Gateway class, it has ‘yield gateway’. I understand that when yield is called the block from Person#save is called, but what does ‘gateway’ become in that block? Can you please explain a little with this code example

class Person
  attr_accessor :first_name, :last_name, :ssn
    def save
      Gateway.save do |persist|
       persist.subject = self
       persist.attributes = [:first_name, :last_name, :ssn]
       persist.to = 'http://www.example.com/person'
      end
   end
end


class Gateway
  attr_acessor :subject, :attributes, :to

  def self.save
    gateway = self.new
    yield gateway
    gateway.execute
  end

  def execute
    request = Net::HTTP::Post.new(url.path)
    attribute_hash = attributes.inject({}) do | result, attribute |
        result[attribute.to_s] = subject.send attribute
        result
      end
      request.set_form(attribute_hash)
      Net::HTTP.new(url.host, url.post).start { |http| http.request(request) }
   end

   def url
     URI.parse(to)
   end

end

Answer 1

The argument to yield will be parsed as an argument to the block. So in your example gateway‘s value is assigned to the persist parameter of the block.