print
package main

import "fmt"

type T struct {
	x int
}

func (t T) String() string { return "boo" }

func main() {
	t := T{123}
	fmt.Printf("%v\n", t)
	fmt.Printf("%#v\n", t)
}
Answer
Try it
boo
main.T{x:123}
print1
package main

import (
	"fmt"
)

func f(a ...int) {
	fmt.Printf("%#v\n", a)
}

func main() {
	f()
}
Answer
Try it
[]int(nil)
race
type Stats struct {
    mutex sync.Mutex

    counters map[string]int
}

func (s *Stats) Snapshot() map[string]int {
    s.mutex.Lock()
    defer s.mutex.Unlock()

    return s.counters
}

func (s *Stats) Add(name string, num int) {
    s.mutex.Lock()
    defer s.mutex.Unlock()
    s.counters[name] = num
}
Answer
func (s *Stats) Snapshot() map[string]int {
	s.mutex.Lock()
	defer s.mutex.Unlock()

result := make(map[string]int, len(s.counters))
for k, v := range s.counters {
	result[k] = v
}
return result

}

select
package main

import "sync"

func main() {
	var wg sync.WaitGroup
	foo := make(chan int)
	bar := make(chan int)
	wg.Add(1)
	go func() {
		defer wg.Done()
		select {
		case foo <- <-bar:
		default:
			println("default")
		}
	}()
	wg.Wait()
}
Answer
Try it
fatal error: all goroutines are asleep - deadlock!
select1
package main

import "fmt"

func main() {
	ch1 := make(chan int)
	ch2 := make(chan int)
	go func() {
		ch1 <- 1
	}()

	go func() {
		select {
		case <-ch1:
		case ch2 <- 2:
		}
	}()

	fmt.Println(<-ch2)
}
  • A. 1
  • B. 2
  • C. No output, program is deadlocked
  • D. No output, program has finished execution.
  • E. else
Answer
Try it
B
slice
package main

import (
	"fmt"
)

func main() {
	var s1 []int
	var s2 = []int{}
	if __ == nil {
		fmt.Println("nil slice")
	}
	if __ != nil {
		fmt.Println("empty slice")
	}
}
  • A. s1, s2
  • B. s2, s1
  • C. s1, s1
  • D. s2, s2
Answer
Try it
A
slice1
package main

import (
	"fmt"
)

func main() {
	s := [3]int{1, 2, 3}
	a := s[:0]
	b := s[:2]
	c := s[1:2:cap(s)]
	fmt.Println(len(a), cap(a))
	fmt.Println(len(b), cap(b))
	fmt.Println(len(c), cap(c))
}
Answer
Try it
0 3
2 3
1 2
slice2
package main

import "fmt"

func main() {
	s1 := []int{1, 2, 3}
	s2 := s1[1:]
	s2[1] = 4
	fmt.Println(s1)
	s2 = append(s2, 5, 6, 7)
	fmt.Println(s1)
}
Answer
Try it
[1 2 4]
[1 2 4]
variable
  • A. p.name
  • B. (&p).name
  • C. (*p).name
  • D. p->name
Answer
AC
variable1
package main

import (
	"fmt"
)

func main() {
	var ans float64 = 15 + 25 + 5.2
	fmt.Println(ans)
}
  • A. 45
  • B. 45.0
  • C. 45.2
  • D. compliation error
Answer
Try it
C
variable2
package main

import (
	"fmt"
)

func main() {
	var ans float64 = 3 / 2
	fmt.Println(ans)
}
  • A. 1.5
  • B. 1
  • C. 0
  • D. compliation error
Answer
Try it
B
variable3
package main

func main() {
	const a int8 = -1
	var b int8 = -128 / a

	println(b)
}
Answer
Try it
compliation error
-128 / a (constant 128 of type int8) overflows int8
variable4
package main

func main() {
	var a int8 = -1
	var b int8 = -128 / a

	println(b)
}
Answer
Try it
-128
variable5
package main

import "fmt"

type MyInt1 int
type MyInt2 = int

func main() {
	var i int =0
	var i1 MyInt1 = i
	var i2 MyInt2 = i
	fmt.Println(i1, i2)
}
Answer
Try it
compilation error
cannot use i (variable of type int) as MyInt1 value in variable declaration
variable6
package main

import "fmt"

func main() {
	const X = 7.0
	var x interface{} = X
	if y, ok := x.(int); ok {
		fmt.Println(y)
	} else {
		fmt.Println(int(y))
	}
}
  • A. 7
  • B. 7.0
  • C. 0
  • D. compilation error
Answer
Try it
C