Learn to Program, 3rd Edition

Methods That Take Procs

When you pass a proc into a method, you can control when the proc is called, how many times it’s called, or even if it’s called at all. For example, let’s say you want to do something before and after some code runs:

def do_self_importantly(some_proc) 
  puts "Everybody just HOLD ON! I'm doing something..."
  some_proc.call
  puts "OK everyone, I'm done. As you were."
end

say_hello = Proc.new do
  puts "hello"
end

say_goodbye = Proc.new do
  puts "goodbye"
end

do_self_importantly(say_hello)
do_self_importantly(say_goodbye)

Everybody just HOLD ON! I'm doing something...
hello
OK everyone, I'm done. As you were.
Everybody just HOLD ON! I'm doing something... ...