Closures

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

package main

import "fmt"

// This function intSeq returns another function
// which we define anonymously in the body of intSeq
// The returned function closes over the variable i to form a closure.
func intSeq() func() int {
    i := 0
    return func() int {
        i++
        return i
    }
}

func main() {

    // We call intSeq, assigning the result
    // (a function) to nextInt. This function value
    // captures its own i value, which will be updated each time we call nextInt.
    nextInt := intSeq()

    // See the effect of the closure by calling nextInt a few times.
    fmt.Println(nextInt())
    fmt.Println(nextInt())
    fmt.Println(nextInt())

    // To confirm that the state is unique to
    // that particular function, create and test a new one.
    newInts := intSeq()
    fmt.Println(newInts())
}

$ go run closures.go
1
2
3
1

The last feature of functions we’ll look at for now is recursion.