It’s been a while since I’ve worked with inheritance and immediately I’m running into one headache of an issue. What am I doing wrong?
Context
Based on the example classes below, I want Derived to inherit the properties & functions of Base through the use of metatables.
Each of these classes reside in their own ModuleScript instance and their type must be referable through a <module>.Class syntax.
Problem
Accessing a member of the Base class within a function defined on Derived through the self argument results in a “Type does not have key” error, despite autocomplete’s ability to show the correct member and type. How come?
Repro
Base
--!strict
const Base = {}
Base.__index = {}
export type Class = setmetatable<{
read instance: Instance,
}, typeof(Base)>
function Base.new(instance: Instance): Class
return setmetatable({
instance = instance,
}, Base)
end
function Base.ChangeName(self: Class, name: string): ()
error("Override required.")
end
return Base
Derived
--!strict
const Base = require(script.Parent.Base)
const Derived = setmetatable({}, Base)
Derived.__index = Derived
export type Class = setmetatable<Base.Class & {
-- ...add new members here.
}, typeof(Derived)>
function Derived.new(instance: Instance): Class
return table.freeze(setmetatable(Base.new(instance), Derived))
end
function Derived.ChangeName(self: Class, name: string): ()
self.instance.Name = name -- TypeError: Type 'Class' does not have key 'instance'
end
return Derived