LearnEnhanced Enums with Fields, Methods & Patterns

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Lesson 36 of 59

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Enhanced Enums with Fields, Methods & Patterns

In Plain English

In modern Dart, **Enhanced Enums** behave like full-fledged immutable classes. Enums can declare final fields, custom `const` constructors, getters, methods, and implement interfaces. Combined with Dart 3 switch expressions, enhanced enums provide exhaustive, bulletproof state representations.

The Mental Model

"Enhanced enums are like official military ranks: not only is each rank distinct in name (Captain, Major, General), but each rank comes with specific assigned salary grades, authority levels, and insignia."

Deep Dive: How It Works

Fields and Constructors: `enum Status { ok(200), err(500); final int code; const Status(this.code); }`.

Instance Methods: Enums can declare methods and computed properties.

Values List: `EnumName.values` provides an unmodifiable list of all declared enum variants.

Syntax Blueprint

enum Priority {
  low(1), medium(2), high(3);
  final int level;
  const Priority(this.level);
  bool get isUrgent => level >= 3;
}

Enhanced enum with fields, const constructor, and computed getter.

Core Rules to Remember

Full Class Capabilities: Enums support fields, methods, getters, and interface implementations.

Exhaustive Matching: Switches over enums are checked by the compiler for 100% case coverage.

Singletons per Variant: Enum members are compile-time singletons, allowing fast `==` equality checks.

Common Beginner Traps & How to Fix Them

Mistake:Attempting to add non-final fields to an enum.

Why it happens: Enum members are compile-time constants and must remain deeply immutable.

How to fix: Ensure all enum fields are declared `final`.

Pro Tip: Use enhanced enums with switch expressions to replace multi-class polymorphism for bounded domain types.

Live Interactive Example

Hit Run Code to see it live

Enhanced Enums with Custom Fields and Methods

Python 3.12

Output Console

Click "Run Code" to view the rendered output.

How it works: Iterated through HttpMethod enum values displaying computed descriptions.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Define Plan Tier Enhanced Enum

Create `enum Plan { free(0), pro(29); final int price; const Plan(this.price); }`.
In `main()`, print `Pro Plan: $${Plan.pro.price}/mo`.

Sandbox Output

Click "Run & Check" to test your solution.

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