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10. Models vs classes

Incan has two “types with fields”:

  • model: data-first (great for DTOs, configs, payloads)
  • class: behavior-first (methods + possible mutation)

Coming from Python?

A model is closest to a Python @dataclass (or a Pydantic Basemodel) in spirit: you declare fields, and you get a constructor automatically.

In Incan you don’t write an __init__/init method. You construct values with keyword arguments matching the declared fields (as shown below), and you can give fields default values in the declaration when needed. For validation or alternate construction, write a separate helper/factory function (often returning Result).

A simple model

model User:
    name: str
    age: int

def main() -> None:
    u = User(name="Alice", age=30)
    println(f"{u.name} age={u.age}")

A simple class

class Counter:
    value: int

    def increment(mut self) -> None:
        self.value += 1

def main() -> None:
    c = Counter(value=0)
    c.increment()
    c.increment()
    println(f"value={c.value}")  # outputs: value=2

Try it

  1. Create a model Product with name and price.
  2. Create a class Cart with a list of products and a method to compute a total.
  3. Print the total.
One possible solution 
model Product:
    name: str
    price: float

class Cart:
    items: list[Product]

    def total(self) -> float:
        total = 0.0
        for item in self.items:
            total = total + item.price
        return total

def main() -> None:
    cart = Cart(items=[
        Product(name="Book", price=10.0),
        Product(name="Pen", price=2.5),
    ])
    println(f"total={cart.total()}")

Where to learn more

Next

Back: 9. Enums and better match

Next chapter: 11. Traits and derives