go类型的默认值，注意pointer, channel, func, interface, map, or slice在没初始化的情况下

nil is a predeclared identifier representing the zero value for a pointer, channel, func, interface, map, or slice type.
Type must be a pointer, channel, func, interface, map, or slice type

package main

import "fmt"



func main() {
   var slic []string
   var m map[string]interface{}
   var i interface{}
   var ptr *int
   var c chan string
   var f func()
   var s *struct{}
   fmt.Println(slic,m,i,ptr,c,f,s)
   if slic == nil{
      fmt.Println("true")
   }
   if m == nil{
      fmt.Println("true")
   }


}
//reset

[] map[] <nil> <nil> <nil> <nil> <nil>
true
true

进程 已完成，退出代码为 0

 

 

 

package main

import "fmt"

type Tess struct {
   s string
   i int
}




func main() {

   var s Tess   //空值 等于  Tess{}    { 0}
   var ptr *Tess  //指针  <nil>
   var ss = Tess{} //空值 等于 var s Tess   { 0}
   var prr = new(Tess) //&{ 0}
   var sss = Tess{  // {test 100}
      s: "test",
      i: 100,
   }
   var slic []int   //nil 值  = []  //  nil值
   var slicc = make([]int,0)  //空值   []
   var slicccc= make([]int,5)  //零值   [0 0 0 0 0]

   fmt.Println(s,ss,sss,ptr,prr)
   fmt.Println(slic,slicc,slicccc)

   var m map[string]string   //map[]  //nil值
   var mm = make(map[string]string)// map[] 空值
   var mmm = map[string]string{"test":"test"}  //map[test:test]
   var mmmm = map[string]string{}  //map[]   空值
   fmt.Println(m,mm,mmm,mmmm)
   var c chan string
   fmt.Println(c)   //<nil>
   c = make(chan string,1)

    fmt.Println("空值",c)  //空值 0xc0000441e0

   c <-"test"
   cc:= <- c
   fmt.Println(cc)  //test
   for i :=range cc{
      fmt.Println(i)
      // 0
      // 1
      // 2
      // 3
   }
   var f func()   //函数
   var ff = func() {
      fmt.Println("OK")
   }
   fmt.Println(f)  //nil
   fmt.Println(ff) // 0xb3cae0

}

结果

{ 0} { 0} {test 100} <nil> &{ 0}
[] [] [0 0 0 0 0]
map[] map[] map[test:test] map[]
<nil>
test
0
1
2
3
<nil>
0x32cae0