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course/10-advanced_functions/exercises/4-defer/code.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+	"fmt"
+	"sort"
+)
+
+const (
+	logDeleted  = "user deleted"
+	logNotFound = "user not found"
+	logAdmin    = "admin deleted"
+)
+
+func logAndDelete(users map[string]user, name string) (log string) {
+	user, ok := users[name]
+	if !ok {
+		delete(users, name)
+		return logNotFound
+	}
+	if user.admin {
+		return logAdmin
+	}
+	delete(users, name)
+	return logDeleted
+}
+
+// don't touch below this line
+
+type user struct {
+	name   string
+	number int
+	admin  bool
+}
+
+func test(users map[string]user, name string) {
+	fmt.Printf("Attempting to delete %s...\n", name)
+	defer fmt.Println("====================================")
+	log := logAndDelete(users, name)
+	fmt.Println("Log:", log)
+}
+
+func main() {
+	users := map[string]user{
+		"john": {
+			name:   "john",
+			number: 18965554631,
+			admin:  true,
+		},
+		"elon": {
+			name:   "elon",
+			number: 19875556452,
+			admin:  true,
+		},
+		"breanna": {
+			name:   "breanna",
+			number: 98575554231,
+			admin:  false,
+		},
+		"kade": {
+			name:   "kade",
+			number: 10765557221,
+			admin:  false,
+		},
+	}
+
+	fmt.Println("Initial users:")
+	usersSorted := []string{}
+	for name := range users {
+		usersSorted = append(usersSorted, name)
+	}
+	sort.Strings(usersSorted)
+	for _, name := range usersSorted {
+		fmt.Println(" -", name)
+	}
+	fmt.Println("====================================")
+
+	test(users, "john")
+	test(users, "santa")
+	test(users, "kade")
+
+	fmt.Println("Final users:")
+	usersSorted = []string{}
+	for name := range users {
+		usersSorted = append(usersSorted, name)
+	}
+	sort.Strings(usersSorted)
+	for _, name := range usersSorted {
+		fmt.Println(" -", name)
+	}
+	fmt.Println("====================================")
+}

course/10-advanced_functions/exercises/4-defer/complete.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+	"fmt"
+	"sort"
+)
+
+const (
+	logDeleted  = "user deleted"
+	logNotFound = "user not found"
+	logAdmin    = "admin deleted"
+)
+
+func logAndDelete(users map[string]user, name string) (log string) {
+	defer delete(users, name)
+
+	user, ok := users[name]
+	if !ok {
+		return logNotFound
+	}
+	if user.admin {
+		return logAdmin
+	}
+	return logDeleted
+}
+
+// don't touch below this line
+
+type user struct {
+	name   string
+	number int
+	admin  bool
+}
+
+func test(users map[string]user, name string) {
+	fmt.Printf("Attempting to delete %s...\n", name)
+	defer fmt.Println("====================================")
+	log := logAndDelete(users, name)
+	fmt.Println("Log:", log)
+}
+
+func main() {
+	users := map[string]user{
+		"john": {
+			name:   "john",
+			number: 18965554631,
+			admin:  true,
+		},
+		"elon": {
+			name:   "elon",
+			number: 19875556452,
+			admin:  true,
+		},
+		"breanna": {
+			name:   "breanna",
+			number: 98575554231,
+			admin:  false,
+		},
+		"kade": {
+			name:   "kade",
+			number: 10765557221,
+			admin:  false,
+		},
+	}
+
+	fmt.Println("Initial users:")
+	usersSorted := []string{}
+	for name := range users {
+		usersSorted = append(usersSorted, name)
+	}
+	sort.Strings(usersSorted)
+	for _, name := range usersSorted {
+		fmt.Println(" -", name)
+	}
+	fmt.Println("====================================")
+
+	test(users, "john")
+	test(users, "santa")
+	test(users, "kade")
+
+	fmt.Println("Final users:")
+	usersSorted = []string{}
+	for name := range users {
+		usersSorted = append(usersSorted, name)
+	}
+	sort.Strings(usersSorted)
+	for _, name := range usersSorted {
+		fmt.Println(" -", name)
+	}
+	fmt.Println("====================================")
+}

course/10-advanced_functions/exercises/4-defer/expected.txt

@@ -0,0 +1,19 @@
+Initial users:
+ - breanna
+ - elon
+ - john
+ - kade
+====================================
+Attempting to delete john...
+Log: admin deleted
+====================================
+Attempting to delete santa...
+Log: user not found
+====================================
+Attempting to delete kade...
+Log: user deleted
+====================================
+Final users:
+ - breanna
+ - elon
+====================================

course/10-advanced_functions/exercises/4-defer/readme.md

@@ -0,0 +1,46 @@
+# Defer
+
+The `defer` keyword is a fairly unique feature of Go. It allows a function to be executed automatically *just before* its enclosing function returns.
+
+The deferred call's arguments are evaluated immediately, but the function call is not executed until the surrounding function returns.
+
+Deferred functions are typically used to close database connections, file handlers and the like.
+
+For example:
+
+```go
+// CopyFile copies a file from srcName to dstName on the local filesystem.
+func CopyFile(dstName, srcName string) (written int64, err error) {
+
+  // Open the source file
+  src, err := os.Open(srcName)
+  if err != nil {
+    return
+  }
+  // Close the source file when the CopyFile function returns
+  defer src.Close()
+
+  // Create the destination file
+  dst, err := os.Create(dstName)
+  if err != nil {
+    return
+  }
+  // Close the destination file when the CopyFile function returns
+  defer dst.Close()
+
+  return io.Copy(dst, src)
+}
+```
+
+In the above example, the `src.Close()` function is not called until after the `CopyFile` function was called but immediately before the `CopyFile` function returns.
+
+Defer is a great way to **make sure** that something happens at the end of a function, even if there are multiple return statements.
+
+## Assignment
+
+There is a bug in the `logAndDelete` function, fix it!
+
+This function should *always* delete the user from the user's map, which is a map that stores the user's name as keys. It also returns a `log` string that indicates to the caller some information about the user's deletion.
+
+To avoid bugs like this in the future, instead of calling `delete` before each `return`, just `defer` the delete once at the beginning of the function.
+