package main

import "fmt"

// function add
func add(a,b int) int {
return a + b
}

// 1
func testFunc1() {

// function "add" to var "f1"
// then "f1" is a function
f1 := add

// type of f1 = func(int int) int
fmt.Printf("type of f1 = %T\n",f1)

// call function "f1"
// params are 2 and 5
sum := f1(2,5)

// sum = 7
fmt.Printf("sum = %d\n",sum)

}

// 2
func testFunc2() {

// anonymous function to var "f1",then "f1" is a function
f1 := func(a,b int) int {
    return a + b
}

// type of f1 = function(int,int) int
fmt.Printf("type of f1 = %T\n",f1)

// call function f1,params are 2 and 5
sum := f1(2,sum)

}

// 3
func testFunc3() {
var i = 0

// the statement after "defer" will be pushed into stack first
// so the value of var "i" will be "0"
// defer i = 0
defer fmt.Printf("defer i = %d\n",i)

i = 100

// i = 100
fmt.Printf("i = %d\n",i)

return

}

// 4
func testFunc4() {
var i = 0

// the anonymous function after "defer" will be pushed into stack first
// but at this time,the statement in function will not be pushed into stack
// so at this time the value of var "i" is not specific
// the value of var
// at the end the value of var "i" is 100
defer func() {
    fmt.Printf("defer i = %d\n",i)
}()

i = 100

// i = 100
fmt.Printf("i = %d\n",i)

return

}

func main() {//testFunc1()//testFunc2()//testFunc3()testFunc4()}