# 7. Object-Oriented Programming

STencil has two OOP styles: `class` (explicit `this.`) and `model` (bare fields).

## class — with `this`
```stencil
class Account {
    func init(owner, balance) {   // init = constructor
        this.owner = owner;
        this.balance = balance;
    }
    func deposit(amount) {
        this.balance = this.balance + amount;
    }
    func withdraw(amount) {
        if (amount > this.balance) {
            print("Insufficient funds");
            return null;
        }
        this.balance = this.balance - amount;
    }
    func report() {
        return this.owner + ": " + this.balance;
    }
}

let a = Account("Ember", 100);   // create (also: new Account("Ember", 100))
a.deposit(50);
a.withdraw(30);
print(a.report());     // Ember: 120
print(a.balance);      // 120   (read a field directly)
```

- `init` is the constructor, run automatically on creation.
- `this.field` reads/writes the object's fields.
- `obj.method(args)` calls a method; `obj.field` reads a field.
- Create with `ClassName(args)` or `new ClassName(args)`.

## model — bare fields
A `model` declares fields with optional defaults and lets methods use field names **without** `this.`:
```stencil
model Car {
    marka: string
    mut hiz: int = 0
    init(m) {
        marka = m
    }
    hizlan(x) {
        hiz = hiz + x
        print(marka + " speed: " + hiz)
    }
}

let c = Car("Toyota");
c.hizlan(20);   // Toyota speed: 20
c.hizlan(30);   // Toyota speed: 50
```

## Which to use?
- `class` is explicit and familiar (like most languages).
- `model` is shorter for data-heavy objects.

Both create objects you access with `.field` and `.method()`.

Next: [Stencils — the signature feature](08_stencils.md)