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<!DOCTYPE html>
<html lang=en>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Awesome Go Interview Questions and Answers</title>
<meta content="Go, Golang, Quiz, Interview questions, Awesome" name=description>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
<link rel="stylesheet" href="/assets/style.css">
<script src="https://code.jquery.com/jquery-3.2.1.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<script src="/assets/bs.js"></script>
<script src="/assets/script.js"></script>
</head>
<body>
<div class="bs-docs-header" id="content" tabindex="-1">
<div class="container">
<h1>Awesome Go Interview Questions and Answers</h1>
<a class="github-button" href="https://github.com/goquiz/goquiz.github.io" data-icon="octicon-star" data-show-count="true" aria-label="Star goquiz/goquiz.github.io on GitHub">Star</a>
<a class="github-button" href="https://github.com/goquiz/goquiz.github.io/issues" data-icon="octicon-issue-opened" data-show-count="true" aria-label="Issue huazhihao/goquiz.github.io on GitHub">Issue</a>
<a class="github-button" href="https://github.com/huazhihao" data-show-count="true" aria-label="Follow @huazhihao on GitHub">Follow @huazhihao</a>
</div>
</div>
<div class="container bs-docs-container">
<div class=row>
<div class=col-md-9 role=main>
<div class=bs-docs-section>
<h1 class=page-header id=lang-spec>Language Specification</h1>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/subslice-grow" target="_blank">Report an issue</a>
<h2 id=subslice-grow>Subslice</h2>
<div class="bs-example gq-question">
What will be printed when the code below is executed?
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
import (
"fmt"
)
func main() {
s := []int{1, 2, 3}
ss := s[1:]
ss = append(ss, 4)
for _, v := range ss {
v += 10
}
for i := range ss {
ss[i] += 10
}
fmt.Println(s)
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/short-declairation" target="_blank">Report an issue</a>
<h2 id=short-declairation>Short Declairation</h2>
<div class="bs-example gq-question">
Assuming x is declared and y is not declared, which clauses below are correct?
</div>
<figure class=highlight>
<pre><code class=language-html data-lang=go>
x, _ := f()
x, _ = f()
x, y := f()
x, y = f()
</code></pre>
</figure>
<button type="button" class="btn btn-info gq-anwser-btn">Answer</button>
<figure class="highlight gq-anwser">
<pre><code class=language-html data-lang=go>
x, _ := f() //incorrect
x, _ = f() //correct
x, y := f() //correct
x, y = f() //incorrect
</code></pre>
</figure>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/interface-nil" target="_blank">Report an issue</a>
<h2 id=interface-nil>Nil Interfaces</h2>
<div class="bs-example gq-question">
What will be printed when the code below is executed?
And explain why `println(InitType() == nil)` cannot be compiled?
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
type S struct{}
func (s S) F() {}
type IF interface {
F()
}
func InitType() S {
var s S
return s
}
func InitPointer() *S {
var s *S
return s
}
func InitEfaceType() interface{} {
var s S
return s
}
func InitEfacePointer() interface{} {
var s *S
return s
}
func InitIfaceType() IF {
var s S
return s
}
func InitIfacePointer() IF {
var s *S
return s
}
func main() {
//println(InitType() == nil)
println(InitPointer() == nil)
println(InitEfaceType() == nil)
println(InitEfacePointer() == nil)
println(InitIfaceType() == nil)
println(InitIfacePointer() == nil)
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/map-ok-idiom" target="_blank">Report an issue</a>
<h2 id=map-ok-idiom>Map Ok-Idiom</h2>
<div class="bs-example gq-question">
Correct two mistakes in line A and B.
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
func main() {
var m map[string]int //A
m["a"] = 1
if v := m["b"]; v != nil { //B
println(v)
}
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<button type="button" class="btn btn-info gq-anwser-btn">Answer</button>
<figure class="highlight gq-anwser">
<pre><code class=language-html data-lang=go>
package main
func main() {
m := make(map[string]int)
m["a"] = 1
if v, ok := m["b"]; ok {
println(v)
}
}
</code></pre>
</figure>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/pointer" target="_blank">Report an issue</a>
<h2 id=pointer>Pointers</h2>
<div class="bs-example gq-question">
Fill in the blanks in line A and B, to assure the printed output is "foo"
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
type S struct {
m string
}
func f() *S {
return __ //A
}
func main() {
p := __ //B
print(p.m) //print "foo"
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<button type="button" class="btn btn-info gq-anwser-btn">Answer</button>
<figure class="highlight gq-anwser">
<pre><code class=language-html data-lang=go>
package main
type S struct {
m string
}
func f() *S {
return &S{"foo"} //A
}
func main() {
p := *f() //B
print(p.m) //print "foo"
}
</code></pre>
</figure>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/empty-interface" target="_blank">Report an issue</a>
<h2 id=empty-interface>interface{} Pointers</h2>
<div class="bs-example gq-question">
In line ABCD, which ones of them have syntax issues?
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
type S struct {
}
func f(x interface{}) {
}
func g(x *interface{}) {
}
func main() {
s := S{}
p := &s
f(s) //A
g(s) //B
f(p) //C
g(p) //D
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<button type="button" class="btn btn-info gq-anwser-btn">Answer</button>
<figure class="highlight gq-anwser">
<pre><code class=language-html data-lang=go>
package main
type S struct {
}
func f(x interface{}) {
}
func g(x *interface{}) {
}
func main() {
s := S{}
p := &s
f(s) //A correct
g(s) //B incorrect
f(p) //C correct
g(p) //D incorrect
}
</code></pre>
</figure>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/for-pointer" target="_blank">Report an issue</a>
<h2 id=for-pointer>Temporary Pointer</h2>
<div class="bs-example gq-question">
Explain why the printed output of below are 333, and modify line A to assure 012 is printed.
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
const N = 3
func main() {
m := make(map[int]*int)
for i := 0; i < N; i++ {
m[i] = &i //A
}
for _, v := range m {
print(*v)
}
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<button type="button" class="btn btn-info gq-anwser-btn">Answer</button>
<figure class="highlight gq-anwser">
<pre><code class=language-html data-lang=go>
package main
const N = 3
func main() {
m := make(map[int]*int)
for i := 0; i < N; i++ {
j := int(i)
m[i] = &j
}
for _, v := range m {
print(*v)
}
}
</code></pre>
</figure>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/label-break" target="_blank">Report an issue</a>
<h2 id=label-break>Break Outer Loop</h2>
<div class="bs-example gq-question">
Modify the code below, to exit the outer for-loop?
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
func main() {
for i := 0; i < 3; i++ {
for j := 0; j < 3; j++ {
print(i, ",", j, " ")
break
}
println()
}
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<button type="button" class="btn btn-info gq-anwser-btn">Answer</button>
<figure class="highlight gq-anwser">
<pre><code class=language-html data-lang=go>
package main
func main() {
outer:
for i := 0; i < 3; i++ {
for j := 0; j < 3; j++ {
print(i, ",", j, " ")
break outer
}
println()
}
}
</code></pre>
</figure>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/global-varible" target="_blank">Report an issue</a>
<h2 id=global-varible>Global Varibles</h2>
<div class="bs-example gq-question">
To declare g as a global variable, which clauses below are correct?
</div>
<figure class=highlight>
<pre><code class=language-html data-lang=go>
var g
var g G
var g = G{}
g := G{}
</code></pre>
</figure>
<button type="button" class="btn btn-info gq-anwser-btn">Answer</button>
<figure class="highlight gq-anwser">
<pre><code class=language-html data-lang=go>
var g //incorrect
var g G //correct
var g = G{} //correct
g := G{} //incorrect
</code></pre>
</figure>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/defer-closefile" target="_blank">Report an issue</a>
<h2 id=defer-closefile>Defer Stack</h2>
<div class="bs-example gq-question">
Correct a mistake about defer in the code below
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
import (
"io/ioutil"
"os"
)
func main() {
f, err := os.Open("file")
defer f.Close()
if err != nil {
return
}
b, err := ioutil.ReadAll(f)
println(string(b))
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<button type="button" class="btn btn-info gq-anwser-btn">Answer</button>
<figure class="highlight gq-anwser">
<pre><code class=language-html data-lang=go>
package main
import (
"io/ioutil"
"os"
)
func main() {
f, err := os.Open("file")
if err != nil {
return
}
defer f.Close()
b, err := ioutil.ReadAll(f)
println(string(b))
}
</code></pre>
</figure>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/defer-panic" target="_blank">Report an issue</a>
<h2 id=defer-panic>Panic Stack</h2>
<div class="bs-example gq-question">
What will be printed when the code below is executed?
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
func f1() {
defer println("f1-begin")
f2()
defer println("f1-end")
}
func f2() {
defer println("f2-begin")
f3()
defer println("f2-end")
}
func f3() {
defer println("f3-begin")
panic(0)
defer println("f3-end")
}
func main() {
f1()
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/defer-recover" target="_blank">Report an issue</a>
<h2 id=defer-recover>recover()</h2>
<div class="bs-example gq-question">
What will be printed when the code below is executed?
What will be the exit code after the code below is executed?
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
import "log"
func f() {
defer func() {
if r := recover(); r != nil {
log.Printf("recover:%#v", r)
}
}()
panic(1)
panic(2)
}
func main() {
f()
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/goroutine-closure" target="_blank">Report an issue</a>
<h2 id=goroutine-closure>Goroutine Closures</h2>
<div class="bs-example gq-question">
What will be printed when the code below is executed?
And fix the issue to assure that `len(m)` is printed as 10.
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
import (
"sync"
)
const N = 10
func main() {
m := make(map[int]int)
wg := &sync.WaitGroup{}
mu := &sync.Mutex{}
wg.Add(N)
for i := 0; i < N; i++ {
go func() {
defer wg.Done()
mu.Lock()
m[i] = i
mu.Unlock()
}()
}
wg.Wait()
println(len(m))
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<button type="button" class="btn btn-info gq-anwser-btn">Answer</button>
<figure class="highlight gq-anwser">
<pre><code class=language-html data-lang=go>
package main
import (
"sync"
)
const N = 10
func main() {
m := make(map[int]int)
wg := &sync.WaitGroup{}
mu := &sync.Mutex{}
wg.Add(N)
for i := 0; i < N; i++ {
go func(i int) {
defer wg.Done()
mu.Lock()
m[i] = i
mu.Unlock()
}(i)
}
wg.Wait()
println(len(m))
}
</code></pre>
</figure>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/type-shadowing" target="_blank">Report an issue</a>
<h2 id=type-shadowing>Type Shadowing</h2>
<div class="bs-example gq-question">
What will be printed when the code below is executed?
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
import (
"fmt"
)
type S1 struct{}
func (s1 S1) f() {
fmt.Println("S1.f()")
}
func (s1 S1) g() {
fmt.Println("S1.g()")
}
type S2 struct {
S1
}
func (s2 S2) f() {
fmt.Println("S2.f()")
}
type I interface {
f()
}
func printType(i I) {
fmt.Printf("%T\n", i)
if s1, ok := i.(S1); ok {
s1.f()
s1.g()
}
if s2, ok := i.(S2); ok {
s2.f()
s2.g()
}
}
func main() {
printType(S1{})
printType(S2{})
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/string-bytes" target="_blank">Report an issue</a>
<h2 id=string-bytes>String to Bytes</h2>
<div class="bs-example gq-question">
What will be printed when the code below is executed?
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
func main() {
s := "123"
ps := &s
b := []byte(*ps)
pb := &b
s += "4"
*ps += "5"
b[1] = '0'
println(*ps)
println(string(*pb))
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/mutex-map" target="_blank">Report an issue</a>
<h2 id=mutex-map>Map Mutex</h2>
<div class="bs-example gq-question">
Fix the issue below to avoid "concurrent map writes" error.
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
import (
"math/rand"
"sync"
)
const N = 10
func main() {
m := make(map[int]int)
wg := &sync.WaitGroup{}
wg.Add(N)
for i := 0; i < N; i++ {
go func() {
defer wg.Done()
m[rand.Int()] = rand.Int()
}()
}
wg.Wait()
println(len(m))
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<button type="button" class="btn btn-info gq-anwser-btn">Answer</button>
<figure class="highlight gq-anwser">
<pre><code class=language-html data-lang=go>
package main
import (
"math/rand"
"sync"
)
const N = 10
func main() {
m := make(map[int]int)
wg := &sync.WaitGroup{}
mu := &sync.Mutex{}
wg.Add(N)
for i := 0; i < N; i++ {
go func() {
defer wg.Done()
mu.Lock()
m[rand.Int()] = rand.Int()
mu.Unlock()
}()
}
wg.Wait()
println(len(m))
}
</code></pre>
</figure>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/DeepEqual" target="_blank">Report an issue</a>
<h2 id=DeepEqual>DeepEqual</h2>
<div class="bs-example gq-question">
Explain why the printed output is false?
Modify line A to assure the printed output really equals to equality of the values of x and y.
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
import (
"fmt"
)
type S struct {
a, b, c string
}
func main() {
x := interface{}(&S{"a", "b", "c"})
y := interface{}(&S{"a", "b", "c"})
fmt.Println(x == y) //A
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<button type="button" class="btn btn-info gq-anwser-btn">Answer</button>
<figure class="highlight gq-anwser">
<pre><code class=language-html data-lang=go>
package main
import (
"fmt"
"reflect"
)
type S struct {
a, b, c string
}
func main() {
x := interface{}(&S{"a", "b", "c"})
y := interface{}(&S{"a", "b", "c"})
fmt.Println(reflect.DeepEqual(x, y))
}
</code></pre>
</figure>
<a class="pull-right gq-report-error" href="https://github.com/goquiz/goquiz.github.io/tree/master/_build/directory/lang-spec/Gosched" target="_blank">Report an issue</a>
<h2 id=Gosched>Gosched</h2>
<div class="bs-example gq-question">
Add code in line A to assure that the lowercase letters and capital letters are printed consecutively.
</div>
<figure class="highlight editable">
<textarea rows="15">
package main
import (
"fmt"
"runtime"
"sync"
)
const N = 26
func main() {
const GOMAXPROCS = 1
runtime.GOMAXPROCS(GOMAXPROCS)
var wg sync.WaitGroup
wg.Add(2 * N)
for i := 0; i < N; i++ {
go func(i int) {
defer wg.Done()
// A
fmt.Printf("%c", 'a'+i)
}(i)
go func(i int) {
defer wg.Done()
fmt.Printf("%c", 'A'+i)
}(i)
}
wg.Wait()
}
</textarea>
</figure>
<button type="button" class="btn btn-primary gq-run-btn">Run</button>
<button type="button" class="btn btn-info gq-anwser-btn">Answer</button>
<figure class="highlight gq-anwser">
<pre><code class=language-html data-lang=go>
package main
import (