Golang's pen test questions & interview questions 01

Just a few simple written test questions , Or you can show me the results directly during the interview .
1, Using different goroutine To operate map There will be a problem of thread synchronization , hold map Switch to int , This problem also exists . stay go It's like this .
2, The output value of the following code is ：

 func t(){
    
    jsonStr:=[]byte(`{"age":1}`)
    var value map[string]interface{
    }
    json.Unmarshal(jsonStr,&value)
    age:=value["age"]
    fmt.Println(reflect.TypeOf(age))
    //float64
}

difference ：

func t() {
    
	jsonStr := []byte(`{"age":1}`)
	var value map[string]int

	json.Unmarshal(jsonStr, &value)
	age := value["age"]
	fmt.Println(reflect.TypeOf(age))
	//int
}

3, Is there a problem with the code below , What's the problem

import (
    "sync"
    "fmt"
)
type UserAges struct {
    
    ages map[string] int
    sync.Mutex
}

func (u *UserAges)Add(name string,age int)  {
    
    u.Lock()
    defer u.Unlock()
    u.ages[name] = age
}

func (u *UserAges)Get(name string)int{
    
    if age,ok:=u.ages[name];ok{
    
        return age
    }
    return -1
}

The problem lies in ,ages There is no bag that exposes the outside of the back , Causes the caller to fail to initialize ages.
And then call add Function time , You're going to report a mistake . Investigate the scope of function .

4, What is the output of the following code ?

func TestArrayAndSlice(){
    
    s1:=[]int{
    1,2,3}
    s2:=s1[1:]
    for i:=range s2{
    
        s2[i]+=10
    }
    fmt.Println(s2)
    s2=append(s2, 4)
    for i:=range s2{
    
        s2[i]+=10
    }
    fmt.Println(s2)
}

The output is as follows ： This is used to investigate arrays and slices s2 Intercept s1 Below is 1 And after ; Then perform the operation .

[12 13]
[22 23 14]

5, What does the following code output

func TestDoit(){
    
	doit:= func(arg int) interface{
    }{
    
		var result *struct{
    }=nil	
	    if (arg>0) {
    
	        result = &struct{
    }{
    }
	    }
	    return result
	}
	
	// Output results .
	//-1:result: <nil>  Empty anonymous structure 
	//1://result: &{}  Anonymous address structure 
	if res:=doit(1);res!=nil{
    
	    fmt.Println("result:",res)
	}
}

output:

result: &{
    }

6, What is the output of the following code
// Put it in main inside
// Specifies that only one logical processor can be used , It is convenient to see the scheduling sequence .

func t2(){
    
	
runtime.GOMAXPROCS(1)
wg:=sync.WaitGroup{
    }
wg.Add(20)
//step 1
for i:=0;i<10 ;i++  {
    
    go func() {
    
        fmt.Println("i",i)
        wg.Done()
    }()
}

fmt.Println("--------------------")

//step 2
for j:=0;j<10 ;j++  {
    
    go func(j int) {
    
        fmt.Println("j",j)
        wg.Done()
    }(j)
}
wg.Wait()
}

output:

--------------------
j 9
i 10
i 10
i 10
i 10
i 10
i 10
i 10
i 10
i 10
i 10
j 0
j 1
j 2
j 3
j 4
j 5
j 6
j 7
j 8

This is something to watch out for , first for There are no parameters in the , The second parameter is passed .
So the first one for It's started in the library goroutine With i It's actually in the main thread i;
The reason is 10,( It's also possible that the first few <10); Because it calls i When ,i Has been added to the main thread 10 了 .
And the second one. for Inside i Is passed through parameters , So it will print 0～9;