Welcome back! Today, we'll master what we learned about backward compatibility in practice. Prepare to apply all the knowledge to practical tasks, but first, let's look at two examples and analyze them.
Let's say that initially, we have a complex data processing function designed to operate on a slice of maps map[string]interface{}, applying a transformation that converts all string values within the map to uppercase. Here's the initial version:
Go1package main 2 3import ( 4 "fmt" 5 "strings" 6) 7 8type DataProcessor struct{} 9 10func (d DataProcessor) ProcessData(items []map[string]interface{}) { 11 processedItems := make([]map[string]interface{}, 0) 12 for _, item := range items { 13 processedItem := make(map[string]interface{}) 14 for k, v := range item { 15 if strVal, ok := v.(string); ok { 16 processedItem[k] = strings.ToUpper(strVal) 17 } else { 18 processedItem[k] = v 19 } 20 } 21 processedItems = append(processedItems, processedItem) 22 } 23 for i := 0; i < min(3, len(processedItems)); i++ { 24 fmt.Println("Processed Item:", processedItems[i]) 25 } 26} 27 28func min(a, b int) int { 29 if a < b { 30 return a 31 } 32 return b 33}
We intend to expand this functionality by adding capabilities to filter the items based on a condition and to allow for custom transformations. The aim is to retain backward compatibility while introducing these enhancements. Here's the updated approach using flexible function signatures and closures:
Go1package main 2 3import ( 4 "fmt" 5 "strings" 6) 7 8type DataProcessor struct{} 9 10/* 11 List of data items to be processed, 12 Function to transform each item, 13 Function to determine if the item meets a condition 14*/ 15func (d DataProcessor) ProcessData( 16 items []map[string]interface{}, 17 transform func(map[string]interface{}) map[string]interface{}, 18 condition func(map[string]interface{}) bool) { 19 if condition == nil { 20 condition = func(item map[string]interface{}) bool { return true } 21 } 22 23 if transform == nil { 24 transform = func(item map[string]interface{}) map[string]interface{} { 25 transformed := make(map[string]interface{}) 26 for k, v := range item { 27 if strVal, ok := v.(string); ok { 28 transformed[k] = strings.ToUpper(strVal) 29 } else { 30 transformed[k] = v 31 } 32 } 33 return transformed 34 } 35 } 36 37 processedItems := make([]map[string]interface{}, 0) 38 for _, item := range items { 39 if condition(item) { 40 processedItems = append(processedItems, transform(item)) 41 } 42 } 43 44 for i := 0; i < min(3, len(processedItems)); i++ { 45 fmt.Println("Processed Item:", processedItems[i]) 46 } 47} 48 49// Usage examples: 50func main() { 51 data := []map[string]interface{}{ 52 {"name": "apple", "quantity": 10}, 53 {"name": "orange", "quantity": 5}, 54 } 55 56 processor := DataProcessor{} 57 58 // Default behavior - convert string values to uppercase 59 processor.ProcessData(data, nil, nil) 60 61 // Custom filter - select items with a quantity greater than 5 62 processor.ProcessData(data, nil, func(item map[string]interface{}) bool { 63 return item["quantity"].(int) > 5 64 }) 65 66 // Custom transformation - convert names to uppercase and multiply the quantity by 2 67 processor.ProcessData(data, func(item map[string]interface{}) map[string]interface{} { 68 transformed := make(map[string]interface{}) 69 for k, v := range item { 70 if k == "name" { 71 transformed[k] = strings.ToUpper(v.(string)) 72 } else if k == "quantity" { 73 transformed[k] = v.(int) * 2 74 } else { 75 transformed[k] = v 76 } 77 } 78 return transformed 79 }, nil) 80}
In this evolved version, we've introduced flexible function signatures that allow users to provide transformation and filtering functions as needed. The default behavior processes all items, converting string values to uppercase, ensuring that the original functionality's behavior is maintained for existing code paths. This robust enhancement strategy facilitates adding new features to a function with significant complexity while preserving backward compatibility, showcasing an advanced application of evolving software capabilities responsively and responsibly.
Imagine now that we are building a music player, and recently, market demands have grown. Now, users expect support not just for MP3 and WAV but also for FLAC files within our music player system. This development poses a unique challenge: How do we extend our music player's capabilities to embrace this new format without altering its established interface or the adapter we've already implemented for WAV support?
Let's say that we currently have a MusicPlayer struct that can only play MP3 files:
Go1package main 2 3import ( 4 "fmt" 5 "strings" 6) 7 8type MusicPlayer struct{} 9 10func (mp MusicPlayer) Play(file string) { 11 if strings.HasSuffix(file, ".mp3") { 12 fmt.Println("Playing", file, "as mp3.") 13 } else { 14 fmt.Println("File format not supported.") 15 } 16}
Let's approach this challenge by introducing a composite adapter, a design that encapsulates multiple strategies to extend functionality in a modular and maintainable manner.
Go1package main 2 3import ( 4 "fmt" 5 "strings" 6) 7 8type MusicPlayerAdapter struct { 9 player *MusicPlayer 10 formatAdapters map[string]func(string) 11} 12 13func NewMusicPlayerAdapter(player *MusicPlayer) *MusicPlayerAdapter { 14 a := &MusicPlayerAdapter{ 15 player: player, 16 formatAdapters: map[string]func(string){ 17 ".wav": ConvertAndPlayWav, 18 ".flac": ConvertAndPlayFlac, 19 }, 20 } 21 return a 22} 23 24func (a *MusicPlayerAdapter) Play(file string) { 25 // Extract the file extension by finding the last dot. 26 extensionIndex := strings.LastIndex(file, ".") 27 if extensionIndex != -1 { 28 extension := strings.ToLower(file[extensionIndex:]) 29 if adapterFunc, exists := a.formatAdapters[extension]; exists { 30 adapterFunc(file) 31 } else { 32 a.player.Play(file) 33 } 34 } else { 35 a.player.Play(file) // No extension found 36 } 37} 38 39func ConvertAndPlayWav(file string) { 40 // Simulate conversion 41 convertedFile := strings.Replace(file, ".wav", ".mp3", 1) 42 fmt.Println("Converting", file, "to", convertedFile, "and playing as mp3...") 43} 44 45func ConvertAndPlayFlac(file string) { 46 // Simulate conversion 47 convertedFile := strings.Replace(file, ".flac", ".mp3", 1) 48 fmt.Println("Converting", file, "to", convertedFile, "and playing as mp3...") 49} 50 51// Upgraded music player with enhanced functionality through the composite adapter 52func main() { 53 legacyPlayer := &MusicPlayer{} 54 enhancedPlayer := NewMusicPlayerAdapter(legacyPlayer) 55 enhancedPlayer.Play("song.mp3") // Supported directly 56 enhancedPlayer.Play("song.wav") // Supported through adaptation 57 enhancedPlayer.Play("song.flac") // Newly supported through additional adaptation 58}
This sophisticated adaptation strategy ensures that we can extend the MusicPlayer to include support for additional file formats without disturbing its original code or the initial adapter pattern's implementation. The MusicPlayerAdapter thus acts as a unified interface to the legacy MusicPlayer, capable of handling various formats by determining the appropriate conversion strategy based on the file type.
Great job! You've delved into backward compatibility while learning how to utilize interfaces, closures, and the Adapter Design Pattern in Go. Get ready for some hands-on practice to consolidate these concepts! Remember, practice makes perfect. Happy Coding!
