Private Fields

Use private to hide a struct field from outside code.

struct User {
    name: string
    private password: string
}

Private fields cannot be read or modified directly from outside the implementation context.

let user = User()

user.name = "Martin"

// Error:
user.password = "secret"

Access Private Fields in impl

Methods inside impl can control access to private fields.

struct User {
    name: string
    private password: string
}

impl User {
    fn setPassword(self: User, password: string) void {
        self.password = password
    }

    fn checkPassword(self: User, password: string) bool {
        return self.password == password
    }
}

Usage:

let user = User()
user.name = "Martin"

user.setPassword("secret")

println(user.checkPassword("secret"))

Why Use Private Fields?

Private fields are useful for values that should not be changed freely.

Examples:

• passwords
• tokens
• cached internal values
• file handles
• database connections
• internal state flags

Private Fields and String Output

Private fields are marked as private in inspection output and skipped by public conversion output.

struct User {
    name: string
    private password: string
}

The runtime treats password differently from public fields.

Private Fields and $convout

The internal $convout hook converts public fields into a dictionary-like output.

Private fields are skipped.

struct User {
    name: string
    private password: string
}

Public output includes name, but not password.

Controlled Updates

Use methods to validate private field updates.

struct Account {
    private balance: int
}

impl Account {
    fn deposit(self: Account, amount: int) void {
        if amount <= 0 {
            panic("amount must be positive")
        }

        self.balance = self.balance + amount
    }

    fn balance(self: Account) int {
        return self.balance
    }
}