Anonymous functions
- Go course
- Beginner
- Lesson 33/90
- 4 min
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 3Every sayacYap() call creates its own independent n.
Practice 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()).
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample 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())
}Expected output
3 2
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What is a closure?
- A function invisible outside the package
- An anonymous function that captures and uses outside variables Correct answer
- A function that ends the program
- A function without parameters
Explanation: A closure accesses the variables where it was defined by reference and keeps them alive even after the outer function returns.
2 Function type
func sayacYap() ____ int {
n := 0
return func() int { n++; return n }
}func sayacYap() func() int {
n := 0
return func() int { n++; return n }
}Explanation: The return type func() int is a function with no parameters that returns an int.
3 Code and meaning
| Term | Meaning |
|---|---|
func(n int) int {...} |
A function value |
func() {...}() |
Called immediately |
n++ (yakalanan) |
Closure state |
func() int |
A function type |