Can Functions Be Passed as Parameters?
In Java I Can Do Something Like Derp(New Runnable { Public Void Run () { /* Run This Sometime Later */ } }) and "Run" the Code in the Method Later. It's a Pain...
In Java I can do something like
derp(new Runnable { public void run () { /* run this sometime later */ } })
and "run" the code in the method later. It's a pain to handle (anonymous inner class), but it can be done.
Does Go have something that can facilitate a function/callback being passed in as a parameter?
8 Answers
Yes, consider some of these examples:
package main
import "fmt"
// convert types take an int and return a string value.
type convert func(int) string
// value implements convert, returning x as string.
func value(x int) string {
return fmt.Sprintf("%v", x)
}
// quote123 passes 123 to convert func and returns quoted string.
func quote123(fn convert) string {
return fmt.Sprintf("%q", fn(123))
}
func main() {
var result string
result = value(123)
fmt.Println(result)
// Output: 123
result = quote123(value)
fmt.Println(result)
// Output: "123"
result = quote123(func(x int) string { return fmt.Sprintf("%b", x) })
fmt.Println(result)
// Output: "1111011"
foo := func(x int) string { return "foo" }
result = quote123(foo)
fmt.Println(result)
// Output: "foo"
_ = convert(foo) // confirm foo satisfies convert at runtime
// fails due to argument type
// _ = convert(func(x float64) string { return "" })
}
Play:
Tour: (Function Closures)
You can pass function as parameter to a Go function. Here is an example of passing function as parameter to another Go function:
package main
import "fmt"
type fn func(int)
func myfn1(i int) {
fmt.Printf("\ni is %v", i)
}
func myfn2(i int) {
fmt.Printf("\ni is %v", i)
}
func test(f fn, val int) {
f(val)
}
func main() {
test(myfn1, 123)
test(myfn2, 321)
}
You can try this out at:
Here is the sample "Map" implementation in Go. Hope this helps!!
func square(num int) int {
return num * num
}
func mapper(f func(int) int, alist []int) []int {
var a = make([]int, len(alist), len(alist))
for index, val := range alist {
a[index] = f(val)
}
return a
}
func main() {
alist := []int{4, 5, 6, 7}
result := mapper(square, alist)
fmt.Println(result)
}
Here is a simple example:
package main
import "fmt"
func plusTwo() (func(v int) (int)) {
return func(v int) (int) {
return v+2
}
}
func plusX(x int) (func(v int) (int)) {
return func(v int) (int) {
return v+x
}
}
func main() {
p := plusTwo()
fmt.Printf("3+2: %d\n", p(3))
px := plusX(3)
fmt.Printf("3+3: %d\n", px(3))
}
This is the simplest way I can come with.
package main
import "fmt"
func main() {
g := greeting
getFunc(g)
}
func getFunc(f func()) {
f()
}
func greeting() {
fmt.Println("Hello")
}
I hope the below example will provide more clarity.
package main
type EmployeeManager struct{
category string
city string
calculateSalary func() int64
}
func NewEmployeeManager() (*EmployeeManager,error){
return &EmployeeManager{
category : "MANAGEMENT",
city : "NY",
calculateSalary: func() int64 {
var calculatedSalary int64
// some formula
return calculatedSalary
},
},nil
}
func (self *EmployeeManager) emWithSalaryCalculation(){
self.calculateSalary = func() int64 {
var calculatedSalary int64
// some new formula
return calculatedSalary
}
}
func updateEmployeeInfo(em EmployeeManager){
// Some code
}
func processEmployee(){
updateEmployeeInfo(struct {
category string
city string
calculateSalary func() int64
}{category: "", city: "", calculateSalary: func() int64 {
var calculatedSalary int64
// some new formula
return calculatedSalary
}})
}
You can also pass the function of a struct, like:
package main
// define struct
type Apple struct {}
// return apple's color
func (Apple) GetColor() string {
return "Red"
}
func main () {
// instantiate
myApple := Apple{}
// put the func in a variable
theFunc := myApple.GetColor
// execute the variable as a function
color := theFunc()
print(color)
}
output will be "Red", check on the playground
Yes Go does accept first-class functions.
See the article "First Class Functions in Go" for useful links.
David Miller brings 15 years of experience in global economics, personal finance strategy, and market dynamics. He specializes in turning complex economic trends into actionable insights for everyday readers.
