Class

A small class system with inheritance. A class is a plain table that also serves as the metatable of its instances, so creating an instance copies nothing and a method lookup costs one step per inheritance level.

New in v4.1.0

MSK.Class has no exports. Use it through the import in your own resource.

Classes work because import.lua compiles the module straight into your resource. The class, its instances and their methods all live in your own Lua runtime.

Instances do not survive an export

FiveM exports only carry plain data. An instance handed through an export arrives without its metatable and therefore without any of its methods. Keep instances inside the resource that created them and pass plain values (ids, tables of fields) across resource boundaries.

MSK.Class.New

Creates a new class, optionally inheriting from parent. The module is callable, so MSK.Class(name, parent) does the same.

Parameters
name - string - Name of the class, used by tostring
parent - table - Optional - A class to inherit from

Returns
class - table - The new class

local class = MSK.Class.New(name, parent)

-- Example
local Vehicle = MSK.Class.New('Vehicle')

function Vehicle:init(model)
    self.model = model
end

function Vehicle:GetModel()
    return self.model
end

local vehicle = Vehicle:New('sultan')
print(vehicle:GetModel()) -- Output: sultan
print(vehicle)            -- Output: Vehicle instance
print(Vehicle)            -- Output: class Vehicle

-- Shorthand (callable module):
local Vehicle = MSK.Class('Vehicle')

Every class has the fields Name and Parent (the parent class or nil).

Class:New

Creates an instance of the class and calls init(self, ...) if the class (or one of its parents) defines it. Calling the class directly, Vehicle(...), does the same.

If init returns exactly false, the construction is refused and nil is returned. That is handy for invalid input.

Parameters
... - any - Optional - Arguments passed to init

Returns
instance - table? - The new instance, or nil if init returned false

local instance = Class:New(...)

-- Example
local Garage = MSK.Class.New('Garage')

function Garage:init(slots)
    if type(slots) ~= 'number' or slots < 1 then
        return false
    end

    self.slots = slots
end

local garage = Garage:New(10) -- instance
local broken = Garage(0)      -- nil

Class:Extend

Creates a child class that inherits every method of this one. Metamethods such as __eq, __lt or __add defined on the parent are copied to the child, because Lua reads them from the metatable itself and not through __index. The generated __tostring is not copied, so a child instance prints its own class name.

Parameters
name - string - Name of the child class

Returns
class - table - The child class

local class = Class:Extend(name)

-- Example
local Car = Vehicle:Extend('Car')

function Car:init(model, doors)
    Car.Parent.init(self, model)
    self.doors = doors
end

local car = Car('sultan', 4)
print(car:GetModel(), car.doors) -- Output: sultan  4

warning

Call the parent through the class name, Car.Parent.init(self, ...), never through self.Parent. self always resolves to the most derived class, so with three levels of inheritance self.Parent.init ends up calling itself until the stack overflows.

Class:IsA

Checks whether an instance or a class is cls or inherits from it.

Parameters
cls - table - The class to check against

Returns
isA - boolean - Whether it is cls or a child of it

local isA = instance:IsA(cls)

-- Example
car:IsA(Car)     -- true
car:IsA(Vehicle) -- true
Car:IsA(Vehicle) -- true
vehicle:IsA(Car) -- false

MSK.Class.IsClass

Checks whether a value is a class created with MSK.Class.New.

Parameters
value - any - The value to check

Returns
isClass - boolean - Whether the value is a class

local isClass = MSK.Class.IsClass(value)

-- Example
MSK.Class.IsClass(Vehicle) -- true
MSK.Class.IsClass(car)     -- false

MSK.Class.IsInstance

Checks whether a value is an instance (not a class) of cls or of one of its children.

Parameters
value - any - The value to check
cls - table - The class to check against

Returns
isInstance - boolean - Whether the value is an instance of cls

local isInstance = MSK.Class.IsInstance(value, cls)

-- Example
MSK.Class.IsInstance(car, Vehicle) -- true
MSK.Class.IsInstance(Car, Vehicle) -- false, Car is a class