Anonymous functions

Learn anonymous functions and the closure concept.

Anonymous functions

Functions without a name can be assigned to a variable, passed as an argument or called right away:

kare := func(n int) int { return n * n }
fmt.Println(kare(4))  // 16

func() {
    fmt.Println("hemen çalıştı")
}()

In Go functions are first-class values: they have types (func(int) int) and are passed around like other values.

A counter with a closure

A function can return another function that captures its local variable. The captured variable is updated on every call:

func sayacYap() func() int {
    n := 0
    return func() int {
        n++
        return n
    }
}

say := sayacYap()
fmt.Println(say(), say(), say())  // 1 2 3

Every sayacYap() call creates its own independent n.

Exercise Closure counter

Write the sayacYap function above. Create two separate counters (a and b); call a twice and b once, then print the next values with fmt.Println(a(), b()).

Show example solution

package main

import "fmt"

func sayacYap() func() int {
    n := 0
    return func() int {
        n++
        return n
    }
}

func main() {
    a := sayacYap()
    b := sayacYap()
    a()
    a()
    b()
    fmt.Println(a(), b())
}

Test yourself

What is a closure?
- A function invisible outside the package
- An anonymous function that captures and uses outside variables
- A function that ends the program
- A function without parameters
Show answer

An anonymous function that captures and uses outside variables — A closure accesses the variables where it was defined by reference and keeps them alive even after the outer function returns.

Function type

func sayacYap() ____ int {
    n := 0
    return func() int { n++; return n }
}

Show answer

func sayacYap() func() int {
    n := 0
    return func() int { n++; return n }
}

Code and meaning

func(n int) int {...}

A function value
func() {...}()

Called immediately
n++ (yakalanan)

Closure state
func() int

A function type

Next lesson: Summary - Functions

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