Closures

Go supports anonymous functions, which can form closures. Anonymous functions are useful when we want to define a function inline without having to name it.

func intSeq() func() int{
  i := 0
  return func() int {
    i++
    return i
  }
}

The function intSeq in the example above returns another function, which we define anonymously in the body of intSeq. The returned function closes over the variable i to form a closure.

nextInt := intSeq() 
fmt.Println(intSeq()) // 1
fmt.Println(intSeq()) // 2
fmt.Println(intSeq()) // 3
newInts := intSeq()
fmt.Println(intSeq()) // 1

Assigning the result of intSeq()(function) to nextInt captures its own i value, which will be updated each time nextInt() is invoked.