Go functions may be closures. A closure is a function value that references variables from outside its body. The function may access and assign to the referenced variables; in this sense the function is "bound" to the variables.

For example, the adder function returns a closure. Each closure is bound to its own sum variable.

package main import "fmt"func adder() func(int) int {    sum := 0    return func(x int) int {        sum += x        return sum    }}func main() {    pos, neg := adder(), adder()    for i := 0; i < 10; i++ {        fmt.Println(            pos(i),            neg(-2*i),            )    }}

A Tour of Go Function closures