errors

Err is interface that implements a single ft that return string

f, err := os.Open("filename.txt")
if err == nil {
    fmt.Println("f")
} else {
    fmt.Println(err)
    //SAME AS
    fmt.Println(err.Error())
}

Creating Errors

import (
    "errors"
)

myError := errors.New("My error string")

Panic, Defer, and Recover

Defer

Puts a func on the call stack that will be run in reverse order when host ft finishes

resp, _ := http.Get("http://golang.org")
defer func () {
   if resp != nil {
      resp.Body.Close()
   }
}()
body, _ := ioutil.ReadAll(resp.Body)

Panic

stops execution passing control to deferred fts

func panic(v interface{})

Recover

Only available in a defer, catch a panic

func Perform() (err error) {
   defer func() {
      if r := recover(); r != nil {
         err = r.(error)
      }
   }()
   GoesWrong()
   return
}
func GoesWrong() {
   panic(errors.New("Fail"))
}
func main() {
   err := Perform()
   fmt.Println(err)
}

Other Examples

attendance := map[string]bool {
    "ann": true,
}
attended, ok := attendance["M"]
if ok {
    fmt.Println("M?", attended)
} else {
    fmt.Println("No info")
}