update ex_2
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@@ -0,0 +1,9 @@
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return SmartLight(id: id, name: name);
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---
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This is poor code naming.
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you should use naming like this.
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if user provides id and name: user_provided_id, user_provided_name
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So I know the relationship.
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@@ -1,114 +1,192 @@
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// WHAT: A mixin is a set of fields and methods that can be reused by multiple classes.
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// WHY: To allow 'SmartSpeaker' to have connection logic without forcing 'SmartLight' to have it.
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mixin Connectable {
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// WHAT: A boolean instance variable initialized to false.
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// WHY: To track whether a specific device is currently linked to a network or bluetooth.
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bool isConnected = false;
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// WHAT: A function using arrow syntax (=>) to negate the current boolean.
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// WHY: Provides a standardized, reusable way to flip the connection state for any class using this mixin.
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void toggleConnection() => isConnected = !isConnected;
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}
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// WHAT: An abstract class acting as a base template.
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// WHY: It defines the shared "DNA" of all devices but prevents anyone from creating a generic "SmartDevice".
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abstract class SmartDevice {
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// WHAT: A final String that can only be set once.
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// WHY: Ensures the device's unique identifier remains immutable (unchangeable) after creation.
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final String id;
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// WHAT: A private String (indicated by the underscore).
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// WHY: Encapsulation; it hides raw data so we can control how it's accessed or formatted via getters/setters.
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String _name;
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// WHAT: Private boolean state for power.
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// WHY: To keep the "ON/OFF" state internal to the object, requiring a method call to change it.
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bool _powerStatus = false;
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// WHAT: Private boolean for automation.
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// WHY: To track if the device should handle its own power timing without user intervention.
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bool _auto_on_off = false;
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// WHAT: A static constant String.
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// WHY: This belongs to the class itself (the brand), not the individual instances.
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static const String brand = "GeminiHome";
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// 1. Standard Constructor with named parameters
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// 1. Standard Constructor
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// WHAT: A generative constructor using 'user_provided' naming.
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// WHY: Maps the external input (user_provided_id) to the internal final field (id).
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SmartDevice({
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required this.id,
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required String name
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}) : _name = name;
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required String user_provided_id,
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required String user_provided_name
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}) : id = user_provided_id,
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_name = user_provided_name;
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// 2. Named Constructor: Preset for Office use
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SmartDevice.office({required this.id})
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: _name = "Office Desk Lamp",
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// 2. Named Constructor: Office
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// WHAT: A specialized constructor for a specific use-case.
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// WHY: It streamlines creation by hardcoding the name and auto-mode for office settings.
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SmartDevice.office({
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required String user_provided_id
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}) : id = user_provided_id,
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_name = "Office Desk Lamp",
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_auto_on_off = true;
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// 3. Named Constructor: Preset for Eco mode
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SmartDevice.eco({required this.id})
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: _name = "Eco Saver Unit",
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// 3. Named Constructor: Eco
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// WHAT: A specialized constructor for power saving.
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// WHY: It ensures the device starts in an "OFF" state with "Auto" mode enabled for efficiency.
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SmartDevice.eco({
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required String user_provided_id
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}) : id = user_provided_id,
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_name = "Eco Saver Unit",
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_powerStatus = false,
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_auto_on_off = true;
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// 4. Factory Constructor using named parameters
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// 4. Factory Constructor
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// WHAT: A factory that decides which subclass to create.
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// WHY: It allows the "SmartDevice" class to return a "SmartLight" or "SmartSpeaker" based on a String input.
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factory SmartDevice.create({
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required String type,
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required String id,
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required String name,
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required String user_provided_type,
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required String user_provided_id,
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required String user_provided_name,
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}) {
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if (type == 'light') return SmartLight(id: id, name: name);
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return SmartSpeaker(id: id, name: name);
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}
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// Specialized factory for the Office preset
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factory SmartDevice.createOffice({required String id}) {
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return SmartLight.office(id: id);
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// WHAT: Logic to check the 'type' string.
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// WHY: To determine which concrete implementation is needed for the user's request.
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if (user_provided_type == 'light') {
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return SmartLight(user_provided_id: user_provided_id, user_provided_name: user_provided_name);
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}
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return SmartSpeaker(user_provided_id: user_provided_id, user_provided_name: user_provided_name);
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}
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// WHAT: A public Getter for the private name.
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// WHY: Allows other parts of the app to read the name without being able to overwrite it directly.
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String get name => _name;
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set name(String value) => _name = value.trim();
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// WHAT: A public Setter with a .trim() method.
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// WHY: Cleans the input data (removing spaces) before saving it to the private '_name' field.
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set name(String user_provided_new_name) => _name = user_provided_new_name.trim();
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// WHAT: An abstract method signature (no curly braces).
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// WHY: It forces every subclass to define what "performing an action" actually means for that specific device.
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void performAction();
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// WHAT: A concrete method shared by all subclasses.
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// WHY: To avoid code duplication; every smart device uses the same logic to toggle power.
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void togglePower() {
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// WHAT: Boolean inversion.
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// WHY: Changes 'true' to 'false' or vice versa to simulate a power switch.
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_powerStatus = !_powerStatus;
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print('$_name is now ${_powerStatus ? "ON" : "OFF"} (Auto-mode: $_auto_on_off)');
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}
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}
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// WHAT: A concrete implementation of a SmartDevice.
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// WHY: To add specific properties (like brightness) that only a light would have.
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class SmartLight extends SmartDevice {
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// WHAT: An integer specific to this class.
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// WHY: To track how bright the light is; initialized to 100 by default.
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int brightness = 100;
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// Using 'super' syntax with named parameters
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// WHAT: Standard constructor passing data to the super class.
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// WHY: To ensure a custom light gets its ID and Name correctly initialized in the base class.
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SmartLight({
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required super.id,
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required super.name
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});
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required String user_provided_id,
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required String user_provided_name
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}) : super(user_provided_id: user_provided_id, user_provided_name: user_provided_name);
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// Redirecting to parent named constructors
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SmartLight.office({required String id}) : super.office(id: id);
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// WHAT: Named constructor with an extra assignment in the initializer list.
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// WHY: It combines the "Office" defaults from the parent with a specific "50%" brightness for this subclass.
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SmartLight.office({
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required String user_provided_id
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}) : brightness = 50, // Sets the brightness specifically for office use.
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super.office(user_provided_id: user_provided_id); // Calls the parent's office logic.
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SmartLight.eco({required String id}) : super.eco(id: id);
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// WHAT: Named constructor for Eco mode.
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// WHY: Redirects to the eco settings in the base class (e.g., auto-off enabled).
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SmartLight.eco({
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required String user_provided_id
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}) : brightness = 20, // WHY: Maybe Eco mode should be even dimmer to save more power!
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super.eco(user_provided_id: user_provided_id);
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@override
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// WHAT: Implementation of the abstract method.
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// WHY: To display the specific state (brightness) of this light.
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void performAction() {
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print('[$_name] Brightness: $brightness%');
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}
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}
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// WHAT: A concrete implementation using inheritance (SmartDevice) and a mixin (Connectable).
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// WHY: To create a device that has a name/id AND the ability to connect/disconnect.
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class SmartSpeaker extends SmartDevice with Connectable {
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// WHAT: A double (0.0 to 1.0) for audio level.
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// WHY: Specific data needed only for audio-based devices.
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double volume;
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// WHAT: Constructor with an assertion check.
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// WHY: The 'assert' stops the program during debugging if the volume is out of bounds (0.0 - 1.0).
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SmartSpeaker({
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required String id,
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required String name,
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required String user_provided_id,
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required String user_provided_name,
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this.volume = 0.5,
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}) : assert(volume >= 0 && volume <= 1.0),
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super(id: id, name: name);
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super(user_provided_id: user_provided_id, user_provided_name: user_provided_name);
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@override
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// WHAT: Concrete implementation of the abstract method.
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// WHY: Defines that for a Speaker, "performing an action" includes checking the connection status.
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void performAction() {
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print('[$_name] Volume: ${(volume * 100).toInt()}%. Connected: $isConnected');
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}
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}
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// --- EXECUTION ---
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void main() {
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// --- USAGE ---
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// 1. Using the 'Office' preset with named ID
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final workLamp = SmartLight.office(id: 'OFFICE_01');
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// WHAT: Instantiating a Light using the Office preset.
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// WHY: To demonstrate how named constructors simplify creating specific device configurations.
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final workLamp = SmartLight.office(user_provided_id: 'OFFICE_01');
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// 2. Using the 'Eco' preset with named ID
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final ecoLight = SmartLight.eco(id: 'ECO_99');
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// WHAT: Instantiating a Light using the Eco preset.
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// WHY: Shows the reuse of the super.eco logic.
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final ecoLight = SmartLight.eco(user_provided_id: 'ECO_99');
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// 3. Standard creation using clear labels for ID and Name
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final customLight = SmartLight(id: 'CUST_01', name: 'My Custom Light');
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// 4. Using the factory with named parameters
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final speaker = SmartDevice.create(
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type: 'speaker',
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id: 'SPK_01',
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name: 'Living Room Bass'
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// WHAT: Standard instantiation of a SmartLight.
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// WHY: Demonstrates creating an object with custom labels.
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final customLight = SmartLight(
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user_provided_id: 'CUST_01',
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user_provided_name: 'My Custom Light'
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);
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// WHAT: Using the factory constructor.
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// WHY: Shows how the 'SmartDevice' base class can act as a single entry point to create different types of objects.
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final speaker = SmartDevice.create(
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user_provided_type: 'speaker',
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user_provided_id: 'SPK_01',
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user_provided_name: 'Living Room Bass'
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);
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// WHAT: Printing and calling methods.
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// WHY: To verify that all constructors and methods are working as expected.
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print('--- Testing Presets ---');
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workLamp.performAction();
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workLamp.togglePower();
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@@ -123,57 +201,6 @@ void main() {
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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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