lua-middleclass-abc

Lua abstract base class implementation for middleclass

Overview

lua-middleclass-abc is just an middleclass class. To mark methods as abstract it must return self.abstractmethod

Method :set_abstract_methods(cls) set all abstract methods in abstract base class. You must mark one or more methods like abstract

Metod :check_abstract_methods(cls) check all methods of subclass. If some abstract methods not implemented ABC raise "Can't instantiate abstract class" error

Simple example

local class = require "middleclass"
local ABC = require "abc"


-- Defines an abstract base class
local AbstractClass = class("AbstractClass", ABC)

function AbstractClass:initialize()
    ABC.initialize(self)
    self:set_abstract_methods(AbstractClass)
end

function AbstractClass:first_method()
    return self.abstractmethod
end

function AbstractClass:second_method()
    return self.abstractmethod
end


-- Define class inheriting from our abstract class
local CorrectConcreteClass = class("CorrectConcreteClass", AbstractClass)

function CorrectConcreteClass:initialize()
    AbstractClass.initialize(self)
    self:check_abstract_methods(CorrectConcreteClass)
end

function CorrectConcreteClass:first_method()
    print("I'm correct first method!")
end

function CorrectConcreteClass:second_method()
    print("I'm correct second method!")
end

-- Define class inheriting from our abstract class without all methods implementation
local IncorrectConcreteClass = class("IncorrectConcreteClass", AbstractClass)

function IncorrectConcreteClass:initialize()
    -- call superclass constructor
    AbstractClass.initialize(self)
    -- check that all abstract methods is overridden
    self:check_abstract_methods(IncorrectConcreteClass)
end

function IncorrectConcreteClass:first_method()
    print("I'm correct first method!")
end


-- Execution:
local c = CorrectConcreteClass()
c:first_method()
c:second_method()
-- Returns:
-- I'm correct first method of instance of class CorrectConcreteClass!
-- I'm correct second method of instance of class CorrectConcreteClass!

local ic = IncorrectConcreteClass()
-- Raise error:
-- Can't instantiate abstract class IncorrectConcreteClass with abstract methods [ second_method,]

Tests

lua-middleclass-abc uses busted for testing