adds error handling

23_error-handling/01_golint/01_before/main.go

@@ -0,0 +1,17 @@
+package main
+
+import "fmt"
+
+func main() {
+	x := 1
+	str := evalInt(x)
+	fmt.Println(str)
+}
+
+func evalInt(n int) string {
+	if n > 10 {
+		return fmt.Sprint("x is greater than 10")
+	} else {
+		return fmt.Sprint("x is less than 10")
+	}
+}

23_error-handling/01_golint/02_after/main.go

@@ -0,0 +1,18 @@
+package main
+
+import "fmt"
+
+func main() {
+	x := 1
+	str := evalInt(x)
+	fmt.Println(str)
+}
+
+func evalInt(n int) string {
+
+	if n > 10 {
+		return fmt.Sprint("x is greater than 10")
+	}
+
+	return fmt.Sprint("x is less than 10")
+}

23_error-handling/02_err-not-nil/01_fmt-println/main.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"os"
+	"fmt"
+)
+
+func main() {
+	_, err := os.Open("no-file.txt")
+	if err != nil {
+		fmt.Println("err happened", err)
+		//		log.Println("err happened", err)
+		//		log.Fatalln(err)
+        //		panic(err)
+	}
+}
+
+// Println formats using the default formats for its operands and writes to standard output.
+
+

23_error-handling/02_err-not-nil/02_log-println/main.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"os"
+	"log"
+)
+
+func main() {
+	_, err := os.Open("no-file.txt")
+	if err != nil {
+		//		fmt.Println("err happened", err)
+		log.Println("err happened", err)
+		//		log.Fatalln(err)
+        //		panic(err)
+	}
+}
+
+/*
+Package log implements a simple logging package ... writes to standard error and prints the date and time of each logged message ... the Fatal functions call os.Exit(1) after writing the log message ... the Panic functions call panic after writing the log message.
+*/
+
+// log.Println calls Output to print to the standard logger. Arguments are handled in the manner of fmt.Println.

23_error-handling/02_err-not-nil/03_log-set-output/log.txt

@@ -0,0 +1 @@
+2016/02/17 04:35:28 err happened open no-file.txt: no such file or directory

23_error-handling/02_err-not-nil/03_log-set-output/main.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"os"
+	"log"
+	"fmt"
+)
+
+func init() {
+	nf, err := os.Create("log.txt")
+	if err != nil {
+		fmt.Println(err)
+	}
+	log.SetOutput(nf)
+}
+
+func main() {
+	_, err := os.Open("no-file.txt")
+	if err != nil {
+		//		fmt.Println("err happened", err)
+		log.Println("err happened", err)
+		//		log.Fatalln(err)
+        //		panic(err)
+	}
+}
+
+/*
+Package log implements a simple logging package ... writes to standard error and prints the date and time of each logged message ... the Fatal functions call os.Exit(1) after writing the log message ... the Panic functions call panic after writing the log message.
+*/
+
+// Println calls Output to print to the standard logger. Arguments are handled in the manner of fmt.Println.

23_error-handling/02_err-not-nil/04_log-fatalln/main.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"os"
+	"log"
+)
+
+func main() {
+	_, err := os.Open("no-file.txt")
+	if err != nil {
+		//		fmt.Println("err happened", err)
+		//		log.Println("err happened", err)
+		log.Fatalln(err)
+        //		panic(err)
+	}
+}
+
+/*
+Package log implements a simple logging package ... writes to standard error and prints the date and time of each logged message ... the Fatal functions call os.Exit(1) after writing the log message ... the Panic functions call panic after writing the log message.
+*/
+
+// Fatalln is equivalent to Println() followed by a call to os.Exit(1).

23_error-handling/02_err-not-nil/05_panic/main.go

@@ -0,0 +1,17 @@
+package main
+
+import (
+	"os"
+)
+
+func main() {
+	_, err := os.Open("no-file.txt")
+	if err != nil {
+		//		fmt.Println("err happened", err)
+		//		log.Println("err happened", err)
+		//		log.Fatalln(err)
+        panic(err)
+	}
+}
+
+

23_error-handling/03_custom-errors/01_errors-new/main.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"errors"
+	"log"
+)
+
+func main() {
+	_, err := Sqrt(-10)
+	if err != nil {
+		log.Fatalln(err)
+	}
+}
+
+func Sqrt(f float64) (float64, error) {
+	if f < 0 {
+		return 0, errors.New("norgate math: square root of negative number")
+	}
+	// implementation
+	return 42, nil
+}

23_error-handling/03_custom-errors/02_errors-new_var/main.go

@@ -0,0 +1,38 @@
+package main
+
+import (
+	"errors"
+	"log"
+	"fmt"
+)
+
+var ErrNorgateMath = errors.New("norgate math: square root of negative number")
+
+func main() {
+	fmt.Printf("%T\n", ErrNorgateMath)
+	_, err := Sqrt(-10)
+	if err != nil {
+		log.Fatalln(err)
+	}
+}
+
+func Sqrt(f float64) (float64, error) {
+	if f < 0 {
+		return 0, ErrNorgateMath
+	}
+	// implementation
+	return 42, nil
+}
+
+// see use of errors.New in standard library:
+// http://golang.org/src/pkg/bufio/bufio.go
+// http://golang.org/src/pkg/io/io.go
+
+
+
+
+
+
+
+
+

23_error-handling/03_custom-errors/03_fmt-errorf/main.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"log"
+	"fmt"
+)
+
+func main() {
+	_, err := Sqrt(-10.23)
+	if err != nil {
+		log.Fatalln(err)
+	}
+}
+
+func Sqrt(f float64) (float64, error) {
+	if f < 0 {
+		return 0, fmt.Errorf("norgate math again: square root of negative number: %v", f)
+	}
+	// implementation
+	return 42, nil
+}

23_error-handling/03_custom-errors/04_fmt-errorf_var/main.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"log"
+	"fmt"
+)
+
+func main() {
+	_, err := Sqrt(-10.23)
+	if err != nil {
+		log.Fatalln(err)
+	}
+}
+
+func Sqrt(f float64) (float64, error) {
+	if f < 0 {
+		ErrNorgateMath := fmt.Errorf("norgate math again: square root of negative number: %v", f)
+		return 0, ErrNorgateMath
+	}
+	// implementation
+	return 42, nil
+}

23_error-handling/03_custom-errors/05_custom-type/main.go

@@ -0,0 +1,40 @@
+package main
+
+import (
+	"log"
+	"fmt"
+)
+
+type NorgateMathError struct {
+	lat, long	string
+	err 		error
+}
+
+func (n *NorgateMathError) Error() string {
+	return fmt.Sprintf("a norgate math error occured: %v %v %v", n.lat, n.long, n.err)
+}
+
+func main() {
+	_, err := Sqrt(-10.23)
+	if err != nil {
+		log.Println(err)
+	}
+}
+
+func Sqrt(f float64) (float64, error) {
+	if f < 0 {
+		nme := fmt.Errorf("norgate math redux: square root of negative number: %v", f)
+		return 0, &NorgateMathError{"50.2289 N", "99.4656 W", nme}
+	}
+	// implementation
+	return 42, nil
+}
+
+// see use of structs with error type in standard library:
+// http://www.goinggo.net/2014/11/error-handling-in-go-part-ii.html
+//
+// http://golang.org/pkg/net/#OpError
+// http://golang.org/src/pkg/net/dial.go
+// http://golang.org/src/pkg/net/net.go
+//
+// http://golang.org/src/pkg/encoding/json/decode.go