initial commit

errors/errors.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+)
+
+//In Go its idiomatic to communicate errors via an explicit, seperate return value.
+//this contrasts with the exceptions used in languages like java and Ruby
+//and the verloaded single result/error value sometimes used in C.
+//Go's approach makes it easy to see which functions return errors and to
+//handle them using the same language constructs employed for any other non-error tasks
+
+
+// by convention, errors are the last return value and have type error, a builtin interface
+func f1(arg int) (int,error){
+	if arg == 42 {
+		//errors.New constructs a basic error value with the given error message
+		return -1, errors.New("cant work with 42")
+	}
+	//a nil value in the error position indicates that there was no error
+	return arg + 3, nil
+}
+
+// its possible to use custom types as errors by implementing Error() method on them.
+// Heres a variant on the example above that uses a custom error type
+type argError struct {
+	arg int
+	prob string
+}
+
+func (e *argError) Error() string {
+	return fmt.Sprintf("%d - %s", e.arg, e.prob)
+}
+
+func f2(arg int) (int,error) {
+	if arg == 42 {
+		return -1, &argError{arg, "can't work with it"}
+	}
+	return arg+3,nil
+}
+
+func main(){
+	//The two loops below test out each of our error-returning
+	//functions. Note that the use of an inline error check on the if line is a common idiom in Go code.
+	for _,i := range []int{7,42} {
+		if r,e :=f1(i); e != nil {
+			fmt.Println("f1 failed:",e)
+		} else {
+			fmt.Println("f1 worked:",r)
+		}
+	}
+	for _,i := range []int{7,42} {
+		if r,e := f2(i);e != nil {
+			fmt.Println("f2 failed:",e)
+		} else {
+			fmt.Println("f2 worked:",r)
+		}
+	}
+
+	//if you want to programmatically use the data in a custom error, you'll need to get the error
+	// as an instance of the custom error type via type assertion
+	_, e := f2(42)
+	if ae, ok:= e.(*argError); ok {
+		fmt.Println(ae.arg)
+		fmt.Println(ae.prob)
+	}
+}