函数-> 一等公民
What are first class functions?
A language that supports first class functions allows functions to be assigned to variables, passed as arguments to other functions and returned from other functions. Go has support for first class functions.
一个语言支持first class functions.允许function赋值给一个变量，作为参数传递给其他函数，从其他函数中返回。GO支持first class functions
Anonymous functions
package main
import (
"fmt"
)
func main() {
a := func() {
fmt.Println("hello world first class function")
}
a()
fmt.Printf("%T", a)
}
package main
import (
"fmt"
)
func main() {
func(n string) {
fmt.Println("Welcome", n)
}("Gophers")
}
User defined function types
package main
import (
"fmt"
)
type add func(a int, b int) int
func main() {
var a add = func(a int, b int) int {
return a + b
}
s := a(5, 6)
fmt.Println("Sum", s)
}
Higher-order functions
The definition of Higher-order function from wiki is a function which does at least one of the following
- takes one or more functions as arguments
- returns a function as its result
Passing functions as arguments to other functions
package main
import (
"fmt"
)
func simple(a func(a, b int) int) {
fmt.Println(a(60, 7))
}
func main() {
f := func(a, b int) int {
return a + b
}
simple(f)
}
Returning functions from other functions
package main
import (
"fmt"
)
func simple() func(a, b int) int {
f := func(a, b int) int {
return a + b
}
return f
}
func main() {
s := simple()
fmt.Println(s(60, 7))
}
Closures
Closures are anonymous functions that access the variables defined outside the body of the function. (访问定义在函数体外部的变量
package main
import (
"fmt"
)
func appendStr() func(string) string {
t := "Hello"
c := func(b string) string {
t = t + " " + b
return t
}
return c
}
func main() {
a := appendStr()
b := appendStr()
fmt.Println(a("World"))
fmt.Println(b("Everyone"))
fmt.Println(a("Gopher"))
fmt.Println(b("!"))
}
Hello World
Hello Everyone
Hello World Gopher
Hello Everyone !
Practical use of first class functions
package main
import (
"fmt"
)
type student struct {
firstName string
lastName string
grade string
country string
}
func filter(s []student, f func(student) bool) []student {
var r []student
for _, v := range s {
if f(v) == true {
r = append(r, v)
}
}
return r
}
func main() {
s1 := student{
firstName: "Naveen",
lastName: "Ramanathan",
grade: "A",
country: "India",
}
s2 := student{
firstName: "Samuel",
lastName: "Johnson",
grade: "B",
country: "USA",
}
s := []student{s1, s2}
f := filter(s, func(s student) bool {
if s.grade == "B" {
return true
}
return false
})
fmt.Println(f)
}
package main
import (
"fmt"
)
func iMap(s []int, f func(int) int) []int {
var r []int
for _, v := range s {
r = append(r, f(v))
}
return r
}
func main() {
a := []int{5, 6, 7, 8, 9}
r := iMap(a, func(n int) int {
return n * 5
})
fmt.Println(r)
}
