Value Declaration Syntax

A value declaration defines an immutable data type without identity. It suits coordinates, ranges, identifiers, and other data where equal content means equality.

value Point {
    Integer x
    Integer y
}

Point origin = Point(x: 0, y: 0)

Static rules

A value may declare constructors and constructor overloads; without one it uses field construction. A constructor may initialize fields of its current object, but may not modify other values or carry mutation permission into a lambda. All normally exiting constructor paths must finish field initialization.

value Row<T> {
    List<T> children
    Integer spacing

    Row(List<T> children) {
        this.children = children
        spacing = 0
    }

    Row(List<T> children, Integer spacing) {
        this.children = children
        this.spacing = spacing
    }
}

• Every field must have a non-null type or explicitly be declared nullable.
• Every field must be initialized before construction ends.
• Fields cannot be assigned in place after construction.
• A value cannot inherit a class or be inherited by a class; it may implement an interface.
• Equality and hash derive recursively from every field.

origin.x = 1 // compile error: value fields cannot be modified
origin = Point(x: 1, y: 0) // valid: variable binds to a new value

Copying a value produces logically independent results. The compiler may share structure as long as the program cannot observe shared identity.

Boundary with Class

Use value when methods are needed but identity is not. Use class when object identity and internal mutable state are needed. ref<T> points to value storage locations and is not used for class sharing.