Polymorphism Through Shared Types
Program to a type, not a class.
Polymorphism Through Shared Types is a free Dart Academy lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Dart Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
What Polymorphism Means
Polymorphism lets one type stand in for many. You call a method on a shared type and each object responds in its own way.
Program to a Type
Instead of naming a concrete class, you depend on a shared supertype. Your code works with anything that fits that shape.
void render(Shape s) => print(s.area());A Shared Base Type
Start with an abstract base that declares the common method every subtype will provide differently.
abstract class Shape {
double area();
}Many Subtypes, One Shape
Each subtype implements area its own way, yet all of them are still treated as a Shape.
class Circle extends Shape {
double area() => 28.3;
}Dynamic Dispatch
At runtime Dart picks the real object's method. This dispatch means the same call runs different code per object.
Shape s = Circle();
s.area(); // runs Circle.areaA List of Different Shapes
Because they share a type, you can collect mixed objects in one List and treat them uniformly.
List<Shape> shapes = [Circle(), Square()];Looping Polymorphically
One loop handles every shape. You never branch on the concrete class; the right area just runs.
for (var s in shapes) {
print(s.area());
}Open to Extension
Add a brand-new Shape subtype later and existing loops use it instantly. Polymorphism keeps code open to growth.
class Triangle extends Shape {
double area() => 12.0;
}Interfaces Work the Same Way
Shared types can come from implements too. Any class implementing the interface plugs straight into the same code.
void log(Printable p) => p.printOut();No Type Checks Needed
Good polymorphic code rarely uses is checks. The shared type already guarantees the method exists, keeping logic clean.
Why It Matters
Polymorphism removes long if-else chains and repeated switches. You write flexible code that bends to new types without edits. 🌱
Quick Check
One quick question about polymorphism.
Recap
Polymorphism means programming to a shared type while each object behaves in its own way. It keeps code flexible and open to new subtypes. ✨
Frequently asked questions
Is the “Polymorphism Through Shared Types” lesson free?
Yes — the full text of “Polymorphism Through Shared Types” is free to read here on the web, and the Dart Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Dart Academy course, upgrade to CoddyKit PRO.
What will I learn in “Polymorphism Through Shared Types”?
Program to a type, not a class. You practise Dart Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Dart Academy?
No prior experience is required. Dart Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Polymorphism Through Shared Types” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Dart Academy lesson?
Yes. Every Dart Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Abstract Classes and Abstract Methods
- Implicit Interfaces and implements
- Polymorphism Through Shared Types
- Composition Over Inheritance