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?
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)
type is not mandatory, you can declare the func parameter type directly: func quote123(fn func(int)string) string.
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
type fn func(int) string and then: myString := f(val)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) } 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") } 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)) } 
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
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 }}) } Yes Go does accept first-class functions.
See the article "First Class Functions in Go" for useful links.
containingObject::instanceMethodName): docs.oracle.com/javase/tutorial/java/javaOO/…