In this section, you are going to learn how to implement a Go function that returns another function using the Go code of returnFunction.go, which will be presented in three segments.

The first code segment of returnFunction.go is as follows:

package main 
 
import ( 
   "fmt" 
) 
 
func funReturnFun() func() int { 
   i := 0 
   return func() int { 
         i++ 
         return i * i 
   } 
} 

As you can see from the implementation of funReturnFun(), its return value is an anonymous function!

The second code segment from returnFunction.go contains the following code:

func main() { 
   i := funReturnFun() 
   j := funReturnFun() 

In this code, you call funReturnFun() two times and assign its return value, which is a function, to two separate variables named i and j. As you will see in the output of the program, the two variables are totally unrelated to each other.

The last code section of returnFunction.go follows next:

   fmt.Println("1:", i()) 
   fmt.Println("2:", i()) 
   fmt.Println("j1:", j()) 
   fmt.Println("j2:", j()) 
   fmt.Println("3:", i()) 
} 

So, in this Go code, you use the i variable three times as i() and the j variable two times as j(). The important thing here is that although both i and j were created by calling funReturnFun(), they are totally independent of each other and share nothing. As a result, although their return values come from the same sequence, they do not interfere with each other in any way.

Executing returnFunction.go will produce the following output:

$ go run returnFunction.go
1: 1
2: 4
j1: 1
j2: 4
3: 9

As you can see from the output of returnFunction.go, the value of i in funReturnFun() keeps increasing and does not become 0 after each call either to i() or j().