yeahlol.lua - YEt Another Homespun Lua OOP Library

yeahlol.lua is a tiny, <50 line <1KB class module for Lua designed to imitate Python's class handling. It's heavily inspired by rxi/classic, but aims to provide nicer support for mixins and multiple inheritance.

yeahlol.lua export a single function - the class definition method.

It takes a list of parent classes as an argument, and returns a function that takes a table of attribute definitions. This allows for idiomatic class definitions that imitate most other OOP languages:

class = require "yeahlol"

MyClass = class(Superclass1, Superclass2) {
  attr1 = 1,
  attr2 = 2,

  method = function(self, ...)
    do_stuff()
  end
}

Usage

Throw yeahlol.lua into your project directory and require it:

class = require "yeahlol"

The class function can now be used to define classes:

-- Define a new class
Animal = class() {
  -- Attributes
  species = "animal",

  -- Methods
  walk = function(self)
    print("The " .. self.species .. " walks a couple steps.")
  end,

  -- Magic methods
  __tostring = function(self)
    return self.species
  end
}

Create an instance of a class by calling the class:

-- Instantiate a class
animal = Animal()

You can then use it as expected:

print(animal) -- "animal"
animal:walk() -- "The animal walks a couple steps."

Customizing initialization

Just like in Python, you can define an _init method on your class to assign attributes and do other things on instantiation:

Car = class() {
  _init = function(self, color)
    self.color = color
  end
}

my_car = Car("red")
print(my_car.color) -- red

(Multiple) Inheritance

Multiple inheritance works. The MRO is left-to-right (or, alternately, the superclasses passed earlier override the methods from the later ones).

If you have a class C = class(A, B){}, and A and B both define a method foo, then C.foo is going to use the definition from A.

To refer to the superclass's original method/attribute that you're overriding, use self.super.

PettableMixin = class() {
  texture = "abstract",

  pet = function(self)
    print("You pet the " .. self.species .. ". It's " .. self.texture .. "!")
  end
}

Dog = class(Animal, PettableMixin) {
  species = "dog",
  texture = "fuzzy",

  -- Initializer - gets called on class instantiation.
  -- If you want to modify the creation of the class instance itself, override
  -- `_new()` - just like in Python!
  _init = function(self, name)
    self.name = name
  end,

  bark = function(self)
    print(self.name .. " barks loudly!")
  end,

  __tostring = function(self)
    return self.name
  end
}

fido = Dog("Fido")
fido:bark() -- "Fido barks loudly!"
fido:walk() -- "The dog walks a couple steps"
fido:pet() -- "You pet the dog. It's fuzzy!"

SizedDog = class(Dog) {
  _init = function(self, name, size)
    -- use .super to refer to the parent's methods in a subclass
    self.super._init(self, name)
    self.species = size .. " dog"
  end
}

max = SizedDog("Max", "big")
max:bark() -- "Max barks loudly!"
max:walk() -- "The big dog walks a couple steps."
max:pet() -- "You pet the big dog. It's fuzzy!"

-- You can also define attributes after the class definition:
max.breed = "St. Bernard"
-- Be careful about this!
function SizedDog:__tostring()
  return self.breed
end
print(max) -- "St. Bernard"

-- You can also override instance methods and attributes just as easily, but
-- not magic methods!
function max:print_breed()
  print(self.name .. " is a " .. self.breed)
end

function max:__tostring()
  return "Nope"
end

max:print_breed() -- "Max is a St. Bernard"
print(max) -- "St. Bernard"

License

yeahlol is available under the Mozilla Public License Version 2.0, the full text of which can be found in LICENSE.

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