defstruct1.exs

# my blog  : https://trangell.com/fa/
# public : http://iranonrails.ir

defmodule Attendee do
  defstruct name: "", paid: false, over_18: true

  def may_attend_after_party(attendee = %Attendee{}) do
    attendee.paid && attendee.over_18
  end

  def print_vip_badge(%Attendee{name: name}) when name !=  "" do
    IO.puts "Very cheap badge for #{name}"
  end

  def print_vip_badge(%Attendee{}) do
    raise "missing name for badge"
  end
end





iex(1)> a1 = %Attendee{ name: "rails", over_18: true }
%Attendee{name: "rails", over_18: true, paid: false}
iex(2)> Attendee.may_attend_after_party(a1)
false
iex(3)> a2 = %Attendee{ name: "rails", over_18: true, paid: true }
%Attendee{name: "rails", over_18: true, paid: true}
iex(4)> Attendee.may_attend_after_party(a2)                       
true
iex(5)> Attendee.print_vip_badge(a2)
Very cheap badge for rails
:ok
iex(6)> Attendee.print_vip_badge(a2)
Very cheap badge for rails
:ok
iex(7)> a3 = %Attendee{ name: "", over_18: true, paid: true }     
%Attendee{name: "", over_18: true, paid: true}
iex(8)> Attendee.print_vip_badge(a3)                         
** (RuntimeError) missing name for badge
    defstruct1.exs:16: Attendee.print_vip_badge/1