Can functions be passed as parameters?

Question

In Java I can do something like

derp(new Runnable { public void run () { /* run this sometime later */ } })

and \"run\" the code in the me

Answer 1

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)

}

Answer 2

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: https://play.golang.org/p/9mAOUWGp0k

Answer 3

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
    }})
}

Answer 4

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: http://play.golang.org/p/XNMtrDUDS0

Tour: https://tour.golang.org/moretypes/25 (Function Closures)

Answer 5

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))
    }

Answer 6

Yes Go does accept first-class functions.

See the article "First Class Functions in Go" for useful links.