I never actually used a .lua type file before until recently for saving game data. And I was wondering can I use it as a templete? for example, say a game with many different cars and i want each car to have the basic layout; Speed, Acceleration, Weight, Color, etc. in a Car.lua file.
My real question is, does using the “require “templete.Car”” make a copy of the Car.lua file for the requesting script during run time or is the values in the Car.lua universal across the app? Do they change for everything else that uses it?
I never actually tried it. I’ve only made a save file manager with that doesnt really help in understanding it in that senario.
Requiring a Lua file multiple times always returns the same thing. It is cached by Lua. What you probably want is either a stateless Lua module or more of an OOP style Lua module. The stateless one would look like this:
-- car_stateless.lua
local M = {}
function M.new(speed, acceleration, weight, color)
return {
speed = speed,
acceleration = acceleration,
weight = weight,
color = color
}
end
function M.repaint(car, color)
car.color = color
end
function M.strip_seats(car)
car.weight = car.weight - 50
end
function M.upgrade_engine(car)
car.speed = car.speed + 10
car.acceleration = car.acceleration + 110
end
return M
And used like this:
local car = require "car"
local volvo = car.new(220, 800, 1500, "blue")
local ferrari = car.new(320, 1800, 1100, "red")
car.repaint(ferrari, "yellow")
car.upgrade_engine(volvo)
Or more of an OOP-style:
-- car_oop.lua
local M = {}
function M.new(speed, acceleration, weight, color)
local car = {
speed = speed,
acceleration = acceleration,
weight = weight,
color = color,
}
function car.repaint(color)
car.color = color
end
function car.strip_seats()
car.weight = car.weight - 50
end
function car.upgrade_engine()
car.speed = car.speed + 10
car.acceleration = car.acceleration + 110
end
return car
end
return M
Used like this:
local car = require "car"
local volvo = car.new(220, 800, 1500, "blue")
local ferrari = car.new(320, 1800, 1100, "red")
ferrari.repaint("yellow")
volvo.upgrade_engine()
That’s pretty great, Thank you. I understand Object Oriented Programming because I’m coming from a Java background but what do you mean by using a stateless lua module?
I actually used that term slightly incorrectly. A stateful Lua module is a module where state is stored inside the module itself where as a stateless Lua module contains no state at all, only logic.
I extrapolated from that definition a bit but the meaning is still almost the same.
In my first example the car.lua module contained only functions that take a car object (Lua table) as it’s first argument. The car contains the state while the Lua module provides stateless functions that operate on the car objects.
In my second example I mixed the two. The functions and the state were both stored in the car object (Lua table). This is more akin to how OOP works. The object is an instance of a class and it contains both the state and functions to manipulate the state.
I was looking over then code sample from the OOP example and realized you were calling the functions from the instances instead of the lua module itself. This as well as Lua Tables could come in handy to make a fun light RPG sometime in the future. Thanks again.
Oops, my mistake.
Btw, interesting article, never heard about closure approach. I am pretty sure “Programming in Lua” mention only oop and metatable approach.
I prefer this. More readable. No semi-colon syntax. Easier to encapsulate data if needed. Faster. Only disadvantage is additional memory consumption, but that is usually not a problem unless you have many instances.
