Hash#using

gistfile1.rb

class Hash
  def using(&block)
    values = block.parameters.map do |(type, name)|
      self[name]
    end

    block.call(*values)
  end
end

hash = {
  first_name: "John",
  last_name:  "Smith",
  age: 35,
  # ...
}

hash.using do |first_name, last_name|
  puts "Hello, #{first_name} #{last_name}."
end

circle = {
  radius: 5,
  color: "blue",
  # ...
}

area = circle.using { |radius| Math::PI * radius**2 }