unary operator challenge

unary_operator_challenge.rb

# In case you haven't seen +@ before, it works as a unary operator (as does -@)
# Example:
#
#     a = A.new
#     +a #=> RuntimeError: You must provide a block!
#     a.send(:+@, &proc { "hello world!" }) #=> "hello world!"
class A
  def +@
    if block_given?
      yield
    else
      raise "You must provide a block!"
    end
  end
end

# Challenge: pass a block to method +@ without using :send
# Example:
#     a = A.new
#     +a do
#       "hello world!"
#     end #=> "hello world!"