Lua 5.1 OOP Inheritance example

oop.lua

-- @josefnpat's Lua OOP example

-- Example of base class

local vehicleclass = {
	-- Example of class variable
	_defaultColor = "blue"
}

function vehicleclass.new(init)
	init = init or {}
	self = {}
	
	-- Example of getter/setter
	self.getColor,self.setColor = vehicleclass.getColor,vehicleclass.setColor
	
	-- Example of read only getter
	self._wheels = 4
	self.getWheels = vehicleclass.getWheels
	
	-- Example of private function
	self._isColor = vehicleclass._isColor
	
	-- Example of overloading
	self:setColor(init.color or vehicleclass._defaultColor)
	
	return self
end

function vehicleclass:_isColor(color)
	return type(color)=="string"
end

function vehicleclass:setColor(color)
	assert(self:_isColor(color),"invalid color `"..tostring(color).."`")
	self._color = color
end

function vehicleclass:getColor()
	return self._color
end

function vehicleclass:getWheels()
	return self._wheels
end

--return vehicleclass -- end of module

-- Example of inherited class

local motorcycleclass = {}

function motorcycleclass.new(init)
	init = init or {}
	-- Example of inheriting the vehicle class
	self = vehicleclass.new(init)
	
	-- Example of overloading a private variable
	self._wheels = 2
	
	-- Example of extending vehicle
	self._helmet = init.helmet or true
	self.getHelmet,self.setHelmet = motorcycleclass.getHelmet,motorcycleclass.setHelmet
	
	-- Example of extending the overload
	self:setColor(init.color or "red")
	
	return self
end

function motorcycleclass:getHelmet()
	return self._helmet
end

function motorcycleclass:setHelmet(helmet)
	assert(type(helmet)=="boolean")
	self._helmet = helmet
end

--return motorcycleclass -- end of module

-- Usage example

-- Inclusion of modules:
--vehicleclass = require"vehicleclass"
--motorcycleclass = require"motorcycleclass"

harley = motorcycleclass.new{color="green"}
print("The harley is `"..harley:getColor().."` and has "..harley:getWheels().." wheels")
harley:setColor("red")
print("The harley is now `"..harley:getColor().."` and has "..harley:getWheels().." wheels")

print("The harley "..(harley:getHelmet() and "has" or "does not have").." a helmet")
harley:setHelmet(false)
print("Now, the harley "..(harley:getHelmet() and "has" or "does not have").." a helmet")

bmw = vehicleclass.new{color="blue"}
print("The bmw is `"..bmw:getColor().."` and has "..bmw:getWheels().." wheels")