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Ganesh Kumar
Ganesh Kumar

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Understanding Closures in Go

#go

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In my previous post, I explained how anonymous functions created and understand how it works.

In this article we will understand how closure.

What is closure

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.

How closure is used?

Each time new value updates the sum variable.

Next time when we call the function, it will use the updated value of sum.

So, It remembers the value of sum.


package main

import "fmt"
func adder(x int) func(int) int {
    sum := 0
    return func(y int) int {
        sum += y
        return sum
    }
}


func main() {
   pos,neg := adder(0),adder(0)
   for i := 0; i < 10; i++ {
        fmt.Println(
            pos(i),
            neg(-i),
        )
    }

}
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Output:

gk@jarvis:~/exp/code/rd/go-exmaple$ go run main.go 
0 0
1 -1
3 -3
6 -6
10 -10
15 -15
21 -21
28 -28
36 -36
45 -45
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Fibonacci series

Here is the example of fibonacci series.
initially we are initializing a and b with 0 and 1.

then with each time calling the function it will return the return value of a.

and update the value of a and b.

So, hence creating a fibonacci series.

package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
    a, b := 0, 1
    return func() int {
        ret := a
        a, b = b, a+b
        return ret
    }
}

func main() {
    f := fibonacci()
    for i := 0; i < 10; i++ {
        fmt.Println(f())
    }
}
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Output:

gk@jarvis:~/exp/code/rd/go-exmaple$ go run main.go 
0
1
1
2
3
5
8
13
21
34
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Conclusion

In this article we understood how closure is used. closure is a function value that references variables from outside its body.

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