first

course/11-pointers/exercises/4-nil_dereference/code.go

@@ -0,0 +1,51 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func removeProfanity(message *string) {
+	// ?
+	messageVal := *message
+	messageVal = strings.ReplaceAll(messageVal, "dang", "****")
+	messageVal = strings.ReplaceAll(messageVal, "shoot", "*****")
+	messageVal = strings.ReplaceAll(messageVal, "heck", "****")
+	*message = messageVal
+}
+
+// don't touch below this line
+
+func test(messages []string) {
+	for _, message := range messages {
+		if message == "" {
+			removeProfanity(nil)
+			fmt.Println("nil message detected")
+		} else {
+			removeProfanity(&message)
+			fmt.Println(message)
+		}
+	}
+}
+
+func main() {
+	messages := []string{
+		"well shoot, this is awful",
+		"",
+		"dang robots",
+		"dang them to heck",
+		"",
+	}
+
+	messages2 := []string{
+		"well shoot",
+		"",
+		"Allan is going straight to heck",
+		"dang... that's a tough break",
+		"",
+	}
+
+	test(messages)
+	test(messages2)
+
+}

course/11-pointers/exercises/4-nil_dereference/complete.go

@@ -0,0 +1,53 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+func removeProfanity(message *string) {
+	if message == nil {
+		return
+	}
+	messageVal := *message
+	messageVal = strings.ReplaceAll(messageVal, "dang", "****")
+	messageVal = strings.ReplaceAll(messageVal, "shoot", "*****")
+	messageVal = strings.ReplaceAll(messageVal, "heck", "****")
+	*message = messageVal
+}
+
+// don't touch below this line
+
+func test(messages []string) {
+	for _, message := range messages {
+		if message == "" {
+			removeProfanity(nil)
+			fmt.Println("nil message detected")
+		} else {
+			removeProfanity(&message)
+			fmt.Println(message)
+		}
+	}
+}
+
+func main() {
+	messages := []string{
+		"well shoot, this is awful",
+		"",
+		"dang robots",
+		"dang them to heck",
+		"",
+	}
+
+	messages2 := []string{
+		"well shoot",
+		"",
+		"Allan is going straight to heck",
+		"dang... that's a tough break",
+		"",
+	}
+
+	test(messages)
+	test(messages2)
+
+}

course/11-pointers/exercises/4-nil_dereference/expected.txt

@@ -0,0 +1,10 @@
+well *****, this is awful
+nil message detected
+**** robots
+**** them to ****
+nil message detected
+well *****
+nil message detected
+Allan is going straight to ****
+****... that's a tough break
+nil message detected

course/11-pointers/exercises/4-nil_dereference/readme.md

@@ -0,0 +1,9 @@
+# Nil Pointers
+
+Pointers can be very dangerous.
+
+If a pointer points to nothing (the zero value of the pointer type) then dereferencing it will cause a runtime error (a [panic](https://gobyexample.com/panic)) that crashes the program. Generally speaking, whenever you're dealing with pointers you should check if it's `nil` before trying to dereference it.
+
+## Assignment
+
+Let's make our profanity checker *safe*. Update the `removeProfanity` function. If `message` is `nil`, `return` early to avoid a [panic](https://gobyexample.com/panic). After all, there are no bad words to remove.