Oops

local class = require 'oops'

-- Define a class
local Duck = class {
  __init = function (self)
    self.quacks = 0
  end,

  quack = function (self)
    self.quacks = self.quacks + 1
    print('Quack! Total: ' .. self.quacks .. ' time(s).')
  end,
}

-- Instantiate and use the class
local daffy = Duck()
daffy:quack()

Oops is a lightweight, expressive, class-based OOP system for Lua. It features first-class classes, clean inheritance, and concise syntax — all in pure Lua.

Features

• Class-based single inheritance: class is a factory of objects (instances).
• Classes as expressions (classes can be anonymous, and defined and used on the spot).
• Controlled visibility scope: classes don't have to be global.
• Concise syntax: local Class = class { hello = function (self) print('world!') end }.
• Class fields and methods (a-la Python)
• Full metamethod support with inheritance (operator overloading)
• Minimal runtime overhead

Use

1. $ luarocks install oops
2. local class = require 'oops'

Examples

Inheritance and superclass constructor:

local Person = class {
  __init = function(self, name)
    self.name = name
  end,
}

local Student = class(Person) {
  __init = function(self, name, school)
    self.__super:__init(name)
    self.school = school
  end,
}

print(Student("Ada", "Academy").name)  -- prints: Ada

Anonymous class instance:

local greeter = (class {
  greet = function(self) print("Hello!") end
})()

greeter:greet()  -- prints: Hello!

Runtime type checking:

local class = require("oops").class
local isinstanceof = require("oops").isinstanceof

local A = class {}
local B = class(A) {}

local obj = B()
print(isinstanceof(obj, A))  -- true
print(isinstanceof(obj, B))  -- true

Class fields and methods:

local class = require("oops")

local Counter = class {
  __class = {
    value = 0,

    increment = function(cls)
      cls.value = cls.value + 1
    end,
  },
}

Counter:increment()
Counter:increment()

print("Counter value:", Counter.value)  --> 2

-- Subclass inherits class method, but not shared field
local Sub = class(Counter) {}
Sub:increment()

print("Counter value:", Counter.value)  --> 2
print("Sub value:", Sub.value)          --> 1

Metamethod support:

local Vector = class {
  __init = function(self, x, y)
    self.x, self.y = x, y
  end,

  __add = function(self, other)
    -- note how we're using self.__class to create a new Vector instance, since the
    -- local Vector is not yet defined
    return self.__class(self.x + other.x, self.y + other.y)
  end,

  __eq = function(a, b)
    return a.x == b.x and a.y == b.y
  end,

  __tostring = function(self)
    return "(" .. self.x .. ", " .. self.y .. ")"
  end,
}

local a = Vector(1, 2)
local b = Vector(3, 4)
local c = a + b

print(c)        --> (4, 6)
print(a == b)   --> false

For more examples see `examples/.

Development

To start:

make deps && make all

Performance benchmark:

make perf

To do

• compare with similar libraries

License

BSD 3-clause.