161 lines
5.4 KiB
Dart
161 lines
5.4 KiB
Dart
// A Mixin: Adds specific behavior without being a parent class
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mixin Connectable {
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bool isConnected = false;
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void toggleConnection() => isConnected = !isConnected;
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}
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abstract class SmartDevice {
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final String id; // Final: Set once
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String _name; // Private field (starts with _)
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bool _powerStatus = false;
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static const String brand = "GeminiHome"; // Static: Shared by all instances
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// 1. Generative Constructor
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SmartDevice(this.id, this._name);
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// 2. Named Constructor
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SmartDevice.temp(this.id) : _name = "Unknown Device";
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// 3. Factory Constructor: Decides which subclass to return
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factory SmartDevice.create(String type, String id, String name) {
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if (type == 'light') return SmartLight(id, name);
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return SmartSpeaker(id, name);
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}
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// Getter and Setter
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String get name => _name;
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set name(String value) => _name = value.trim();
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// Abstract method: Must be implemented by children
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void performAction();
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// Regular method
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void togglePower() {
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_powerStatus = !_powerStatus;
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print('$_name is now ${_powerStatus ? "ON" : "OFF"}');
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}
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}
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class SmartLight extends SmartDevice {
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int brightness = 100;
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// Uses 'super' to pass data to the parent constructor
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SmartLight(super.id, super.name);
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@override
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void performAction() {
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print('Adjusting brightness to $brightness%');
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}
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}
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// 'with Connectable' adds the toggleConnection() method to this class
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class SmartSpeaker extends SmartDevice with Connectable {
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double volume;
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// 4. Initializer List: Sets volume before the constructor body runs
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SmartSpeaker(String id, String name, {this.volume = 0.5})
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: assert(volume >= 0 && volume <= 1.0),
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super(id, name);
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// 5. Redirecting Constructor: Forwards to the main constructor
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SmartSpeaker.loud(String id, String name) : this(id, name, volume: 1.0);
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@override
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void performAction() {
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print('Playing music at ${volume * 100}% volume. WiFi: $isConnected');
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}
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}
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void main() {
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// Using the Factory
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final myLight = SmartDevice.create('light', 'L1', 'Living Room Lamp');
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// Using the Redirecting Constructor
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final partySpeaker = SmartSpeaker.loud('S1', 'Bass Blaster');
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myLight.togglePower(); // Parent method
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partySpeaker.toggleConnection(); // Mixin method
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partySpeaker.performAction(); // Overridden method
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}
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// You're absolutely right. Understanding *why* we use these features is more important than just knowing the syntax. Let’s break down the rationale and real-world use cases for the structure I built.
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// ---
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// ## 1. The Abstract Class (`SmartDevice`)
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// **Rationale:** You want to define a "contract." Every smart device must have an ID, a name, and an action, but a "generic" smart device doesn't exist in reality—it’s always a specific light, speaker, or thermostat.
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// * **Use Case:** In a Large App, you might have a `List<SmartDevice> devices`. You can loop through this list and call `.togglePower()` on every item without knowing if it's a light or a speaker. This is the heart of **Polymorphism**.
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// ---
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// ## 2. Factory Constructors (`SmartDevice.create`)
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// **Rationale:** Normal constructors always create a new instance of the exact class they belong to. A `factory` constructor is more flexible: it can return a subclass or even a cached instance.
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// * **Use Case:** **API Parsing.** When you get JSON data from a server, you don't know the device type until you read the data. A factory constructor can look at the "type" field in the JSON and decide to return a `SmartLight` object or a `SmartSpeaker` object automatically.
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// ---
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// ## 3. Mixins (`with Connectable`)
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// **Rationale:** Dart doesn't allow a class to have two parents (Multiple Inheritance) because it gets messy. Mixins allow you to "plug in" shared behavior across unrelated classes.
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// * **Use Case:** Imagine you have a `SmartSpeaker` (a device) and a `PhoneApp` (not a device). Both need "WiFi Connection" logic. Instead of copying the code twice, you create a `Connectable` mixin and apply it to both.
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// ---
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// ## 4. Getters and Setters
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// **Rationale:** This is about **Encapsulation**. You should never let outside code touch your internal variables (`_name`) directly. By using a setter, you can "sanitize" the data.
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// * **Use Case:** Validation. If a user tries to set a device name to a string full of empty spaces, your setter `set name(value) => _name = value.trim();` automatically cleans it up before it’s saved to your database.
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// ---
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// ## 5. Redirecting Constructors (`SmartSpeaker.loud`)
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// **Rationale:** To avoid "Boilerplate" (repetitive code). If you have a common configuration for a class, you don't want to rewrite the initialization logic.
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// * **Use Case:** **Presets.** In a UI, you might have a "Default" button and a "Pro" button. Instead of manually setting 10 different parameters each time, you create a named constructor like `Button.primary()` that redirects to the main constructor with all the "Pro" settings pre-filled.
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// ---
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// ## 6. Static Members (`static const brand`)
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// **Rationale:** Memory efficiency. If you have 1,000 smart lights, you don't need the string "GeminiHome" stored in memory 1,000 times.
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// * **Use Case:** **Configuration & Constants.** Use `static` for things that are "Universal truth" for the class, such as a maximum volume limit or a shared API version number.
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// Would you like me to show you how to handle **Interfaces** in Dart, which is the final piece of the OO puzzle?
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