Function as Arguments
In Go, function is also a type. So we can pass function as another function’s parameters.
當我們將function當成參數使用時，必須在參數列表列出funtion本身的參數type與及其所需的回傳type, 如:
func(int, int) int
Example 1
func print(fn func(int, int) int, a, b int) {
fmt.Println(fn(a, b))
}
func area(a, b int) int {
return a * b
}
func sum(a, b int) int {
return a + b
}
func main() {
print(area, 3, 4) // 12
print(sum, 3, 4) // 7
}
Example 2
func compute(fn func(float64, float64) float64) float64 {
return fn(3, 4)
}
func hypot(x, y float64) float64 {
return math.Sqrt(x*x + y*y)
}
func main() {
fmt.Println(compute(hypot)) // 5
}
Function Closures
Golang supports anonymous functions(匿名函式) which can form closures(閉包). Anonymous functions are useful when you want to define a function inline without having to name it.
Anonymous Function
所謂的匿名函式就是沒有名字的函式
- 匿名函式可以作為返回值
- 匿名函式也可以作為變數
Example
// anonymous function
func(x, y int) int {
return x + y
}
// anonymous function as a return value
func printSum() func(int, int) {
return func(x, y int) {
fmt.Println(x + y)
}
}
// anonymous function as a variable
f := func(x, y int) int {
return x + y
}
- Python’s
lambda
# anonymous function
lambda x, y: x + y
f = lambda x, y: x + y
Closure
A closure is a function value that references variables from outside its body
閉包就是能夠讀取其他函式內部變量的函式。好處是可以把變數隱藏在內部，讓外部存取不到，只能看到我們想要提供的值
Example 1
func intSeq() func() int {
i := 0
return func() int {
i += 1
return i
}
}
func main() {
nextInt := intSeq()
fmt.Println(nextInt()) // 1
fmt.Println(nextInt()) // 2
fmt.Println(nextInt()) // 3
}
上例將變數i隱藏在內部匿名函式中，我們無法對變數i進行操作，只能拿到他的值。
Example 2
func adder() func(int) int {
sum := 0
return func(x int) int {
sum += x
return sum
}
}
- Closure in Python
def printMessage():
string = "This is closure"
def print_msg():
print(string)
return print_msg
Exercise: Fibonacci closure
// fibonacci is a function that returns
// a function that return an int.
func fibonacci() func() int {
a, b := 0, 1
return func() int {
v := a
a, b = b, a+b
return v
}
}