Closures in Ruby

Question

Sample code:

def func(a, &closure)
  return a if a
  closure ||= lambda{ |words| puts "!!! " + words }
  closure.call("1")
  closure.call("2")
end

func(false){ |words| puts "??? " + words }   

Please explain. I can not understand this line:

closure ||= lambda{ |words| puts "!!! " + words }

If you remove || will be permanently displayed as follows: "!!! 1", "!!! 2". Why? And also explain this:

def func(a, &closure)

where did &closure.

Answer 1

def func(a, &closure)
    return a if a
    closure ||= lambda{ |words| puts "!!! " + words }
    closure.call("1")
    closure.call("2")
end

func(false){ |words| puts "??? " + words }   

In "&closure" the ampersand (&) means that the function takes a block as a parameter. What is happening is you are passing a Proc (a block is just a Proc defined with a different syntax) to the func function which is then called with the variable 1 and 2.

The ||= means "or equals." It is used to assign a value to a variable if the current value is nil. It is shorthand for:

closure = lamda{ |words| puts "!!! " + words } if closure.nil

This blog post explains blocks, Procs and lamdas well.