The gideros class system mimics the behavior of Gideros classes. This class system was chosen because, besides from the existing requirements, it represents a typical instance of naively defined class system that can be problematic for the type checker.

A typical declaration for the gideros class system is as follows:

--# class system gideros
--# assume global class(gideros) Object
--# assume global Core: {}
--# assume Core.class: [make_class(gideros)] function(parent: table?) --> table

This defines the Object class and a Core.class class-generating function.

The new method is automatically created when the init method is created.

--# assume global class(gideros) Foo: Object

--v method(text: string)
function Foo:init(text)
    self.text = text
end

local x = Foo.new('string')

Note that the actual creation currently occurs at the first invocation of new, so the error may be delayed to the usage site.

The Gideros class system supports the single inheritance and shares the general syntax and behavior described in the earlier section.

Fields in child classes simply shadows a previously defined field in a parent, which would break the subtyping (using a child class to the place expecting a parent class) if not restricted. Therefore in Kailua fields cannot be normally overriden. The exception is made for constructors (init), which cannot be explicitly called through instances anyway.

In Gideros every class is assumed to be a descendant of the Object class. Kailua recognizes the first (and only) class defined without a parent as such a class and disallows multiple such classes. The Core.class function will use Object as a parent if no other parent is specified. Since this implicit behavior is confusing otherwise, though, --# assume class should always specify the parent class even when it would be Object.