go languages var statement chan, map, pointer, pay attention to the situation

Occur in the processing of timeouts when issues:

Problem code

package main

import(

　　"fmt"

　　"time"

)

func main(){

    var ch chan string
    go func() {
    ch <- "result"
    }()
    select {
    case res := <-ch:
        fmt.Println(res)
        return
    case <-time.After(time.Second * 5):
        fmt.Println("timeout")
    }
}

　Cause of the error: var ch chan string ch no allocation of space, so that has been running the case <- time.After (time.Second * 5) this branch. Solution is added: ch = make (chan string) or delete var ch chan string, add ch: = make (chan string)

Thinking:

　　var should make use of the pointer in a statement, chan, map when it allocated space, or can not use

Realization of comparative map:

var kl map[string]string
kl["string"]="stk"
fmt.Println(kl)  //出现错误

var kt map[string]string
kt = make(map[string]string)
kt["string"] = "strin"
fmt.Println(kt) //正确