いろんな言語でカウンタを書いてみる

counter.js

counter = function() {
  var count = 0;
  return function() {
    return count += 1;
  }
}

c1 = counter()
c1() //=> 1
c1() //=> 2

counter.py

def counter():
    count = [0]
    def f():
        count[0] += 1
        return count[0]
    return f
  
c1 = counter()
c1() #=> 1
c1() #=> 2

counter.scala

def counter() = {
  var count = 0
  val f = () => { count += 1; count }
  f
}

c1 = counter()
c1() //=> 1
c1() //=> 2

counter.swift

func counter() -> () -> Int {
    var count = 0
    func f() -> Int {
        count += 1
        return n
    }
    return f
}

let c1 = counter()
c1() //=> 1
c1() //=> 2

counter_lambda.rb

def counter
  count = 0
  lambda { count += 1; return count }
end

c1 = counter
c1.call #=> 1
c1.call #=> 2

counter_proc.rb

def counter
  count = 0
  Proc.new { count += 1 }
end

c1 = counter
c1.call #=> 1
c1.call #=> 2