package main

import (
 "encoding/json"
 "fmt"
 "reflect"
)

type S struct {
 A []int `json:"a"`
 B []int `json:"b"`
}

func main() {
 var a []int                           // nil
 b := []int{}                          // пустой
 fmt.Println(a == nil, len(a), cap(a)) // ?
 fmt.Println(b == nil, len(b), cap(b)) // ?

 fmt.Println(reflect.DeepEqual(a, b)) // ?

 x := S{A: a, B: b}
 d, _ := json.Marshal(x)
 fmt.Println(string(d))
}

package main

import (
 "fmt"
 "os"
)

func main() {
 var err error = (*os.PathError)(nil)
 fmt.Println(err == nil)
}

package main

import "fmt"

func main() {
 s := []int{1, 2, 3, 4}
 t := s[1:3]         // t = [2, 3]
 t = append(t, 99)   // возможно, меняет s[3]
 s[2] = 42           // изменяем s напрямую

 fmt.Println("s:", s)
 fmt.Println("t:", t)
}

package main

import (
 "errors"
 "fmt"
)

type myError struct{}

func (m *myError) Error() string {
 return "something went wrong"
}

func returnsNilError() error {
 var e *myError = nil
 return e
}

func main() {
 err := returnsNilError()
 fmt.Println("err == nil:", err == nil) // неожиданно false
 fmt.Println("err:", err)
}

package main

import (
 "fmt"
 "runtime"
 "time"
)

func main() {
 runtime.GOMAXPROCS(runtime.NumCPU())

 for i := 0; i < 5; i++ {
  go func(id int) {
   for {
    fmt.Println("goroutine", id, "работает на потоке")
    time.Sleep(200 * time.Millisecond)
   }
  }(i)
 }

 for {
  fmt.Println("горутин сейчас:", runtime.NumGoroutine())
  time.Sleep(time.Second)
 }
}