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// packages_imports.go - Demonstrates Go package imports and usage package main import ( // Standard library imports "fmt" "io" "math" "math/rand" "net/http" "os" "strings" "time" // Aliased imports str "strings" // Dot imports (imports all exported names directly) // . "fmt" // Uncomment to use - not recommended in production // Blank imports (for side effects only) _ "image/png" // Local package import (would be actual import in real project) // "github.com/user/project/module" ) // StandardLibraryUsage demonstrates standard library usage func StandardLibraryUsage() { // fmt package fmt.Println("Hello from fmt") // strings package upper := strings.ToUpper("hello") fmt.Println(upper) // math package sqrt := math.Sqrt(16) fmt.Printf("Square root: %.2f\n", sqrt) // time package now := time.Now() fmt.Println("Current time:", now.Format(time.RFC3339)) // rand package rand.Seed(time.Now().UnixNano()) randomNum := rand.Intn(100) fmt.Println("Random number:", randomNum) } // AliasedImportUsage demonstrates aliased imports func AliasedImportUsage() { // Using str alias for strings package result := str.Contains("hello world", "world") fmt.Println("Contains:", result) trimmed := str.TrimSpace(" spaces ") fmt.Println("Trimmed:", trimmed) } // FileOperations demonstrates os and io packages func FileOperations() error { // Create a file file, err := os.Create("example.txt") if err != nil { return fmt.Errorf("failed to create file: %w", err) } defer file.Close() // Write to file _, err = io.WriteString(file, "Hello, File!\n") if err != nil { return fmt.Errorf("failed to write to file: %w", err) } // Read file content, err := os.ReadFile("example.txt") if err != nil { return fmt.Errorf("failed to read file: %w", err) } fmt.Println("File content:", string(content)) // Clean up os.Remove("example.txt") return nil } // HTTPClientExample demonstrates net/http package func HTTPClientExample() error { // Make HTTP request resp, err := http.Get("https://api.github.com") if err != nil { return fmt.Errorf("failed to make request: %w", err) } defer resp.Body.Close() fmt.Println("Status:", resp.Status) // Read response body body, err := io.ReadAll(resp.Body) if err != nil { return fmt.Errorf("failed to read response: %w", err) } fmt.Println("Response length:", len(body)) return nil } // HTTPServerExample demonstrates creating an HTTP server func HTTPServerExample() { http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) { fmt.Fprintf(w, "Hello, %s!", r.URL.Path[1:]) }) http.HandleFunc("/api/users", handleUsers) // This would start the server (commented out for sample) // http.ListenAndServe(":8080", nil) } func handleUsers(w http.ResponseWriter, r *http.Request) { switch r.Method { case http.MethodGet: fmt.Fprintf(w, "Getting users") case http.MethodPost: fmt.Fprintf(w, "Creating user") default: http.Error(w, "Method not allowed", http.StatusMethodNotAllowed) } } // StringsPackageUsage demonstrates extensive strings package usage func StringsPackageUsage() { // Various string operations text := "Hello, World! Hello, Go!" contains := strings.Contains(text, "World") hasPrefix := strings.HasPrefix(text, "Hello") hasSuffix := strings.HasSuffix(text, "Go!") count := strings.Count(text, "Hello") index := strings.Index(text, "World") split := strings.Split(text, " ") joined := strings.Join(split, "-") replaced := strings.Replace(text, "Hello", "Hi", -1) fmt.Printf("Contains: %v, Prefix: %v, Suffix: %v\n", contains, hasPrefix, hasSuffix) fmt.Printf("Count: %d, Index: %d\n", count, index) fmt.Printf("Split: %v\n", split) fmt.Printf("Joined: %s\n", joined) fmt.Printf("Replaced: %s\n", replaced) } // MathPackageUsage demonstrates math package func MathPackageUsage() { // Math constants fmt.Println("Pi:", math.Pi) fmt.Println("E:", math.E) // Math functions fmt.Println("Sqrt(16):", math.Sqrt(16)) fmt.Println("Pow(2, 10):", math.Pow(2, 10)) fmt.Println("Max(10, 20):", math.Max(10, 20)) fmt.Println("Min(10, 20):", math.Min(10, 20)) fmt.Println("Abs(-42):", math.Abs(-42)) fmt.Println("Ceil(4.2):", math.Ceil(4.2)) fmt.Println("Floor(4.8):", math.Floor(4.8)) fmt.Println("Round(4.5):", math.Round(4.5)) } // TimePackageUsage demonstrates time package func TimePackageUsage() { // Current time now := time.Now() fmt.Println("Current time:", now) // Time formatting formatted := now.Format("2006-01-02 15:04:05") fmt.Println("Formatted:", formatted) // Parsing time parsed, _ := time.Parse("2006-01-02", "2024-01-15") fmt.Println("Parsed:", parsed) // Time arithmetic tomorrow := now.Add(24 * time.Hour) yesterday := now.Add(-24 * time.Hour) fmt.Println("Tomorrow:", tomorrow.Format("2006-01-02")) fmt.Println("Yesterday:", yesterday.Format("2006-01-02")) // Duration duration := 2 * time.Hour fmt.Println("Duration:", duration) // Sleep // time.Sleep(time.Second) } // OSPackageUsage demonstrates os package func OSPackageUsage() { // Environment variables os.Setenv("MY_VAR", "my_value") value := os.Getenv("MY_VAR") fmt.Println("Environment variable:", value) // Command line arguments args := os.Args fmt.Println("Program name:", args[0]) // Working directory wd, _ := os.Getwd() fmt.Println("Working directory:", wd) // File info fileInfo, err := os.Stat("packages_imports.go") if err == nil { fmt.Println("File size:", fileInfo.Size()) fmt.Println("Is directory:", fileInfo.IsDir()) fmt.Println("Modified:", fileInfo.ModTime()) } } // IOPackageUsage demonstrates io package func IOPackageUsage() { // String reader reader := strings.NewReader("Hello from io package") // Read all content, _ := io.ReadAll(reader) fmt.Println("Content:", string(content)) // Copy example (would copy from one reader/writer to another) // io.Copy(dst, src) } // MultiplePackageUsage uses multiple packages together func MultiplePackageUsage() error { // Combine time, strings, and fmt now := time.Now() formatted := now.Format(time.RFC3339) upper := strings.ToUpper(formatted) final := fmt.Sprintf("Current time: %s", upper) // Combine math and fmt result := math.Sqrt(math.Pow(3, 2) + math.Pow(4, 2)) output := fmt.Sprintf("Hypotenuse: %.2f", result) fmt.Println(final) fmt.Println(output) return nil } // PackageInitPattern demonstrates initialization patterns var ( initialized bool config map[string]string ) func init() { // This runs automatically when package is imported initialized = true config = make(map[string]string) config["version"] = "1.0.0" config["env"] = "development" fmt.Println("Package initialized") } // GetConfig returns the config func GetConfig(key string) string { return config[key] } func demonstrateImports() { StandardLibraryUsage() AliasedImportUsage() StringsPackageUsage() MathPackageUsage() TimePackageUsage() OSPackageUsage() IOPackageUsage() MultiplePackageUsage() }