How do methods work in an inherited class?

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#1

I’m currently in the process of learning OOP and I have a very basic example setup and I’m a bit confused about methods in an inherited class. I have an enemy class and then I have a boss class that inherits from enemy (because they’re both enemies, but the boss might have a few differences) is it possible to give the inherited class the same method which does its own thing? So the enemy attack method is the default which gets used if the inherited class doesn’t have its own. Also in the inherited class I added a random IsDeadly variable to it, but I can’t figure out how to access it lol.

local Enemy = {}
Enemy.__index = Enemy

function Enemy.new(Name,HP,MP,Lvl,Model)
    return setmetatable({
        Name = Name,
        HP = HP,
        MP = MP,
        Lvl = Lvl,
        Model = Model
    }, Enemy)
end

--this would be the default
function Enemy:Attack()
    warn("basic attacks")
end

return Enemy

local Enemy = require(game.ServerScriptService.OOPTesting.Enemy)

--Inheritance
local Boss = setmetatable({}, Enemy)
Boss.__index = Boss

function Boss.new(Name,HP,MP,Lvl,Model,IsDeadly)
    local newBoss = Enemy.new(Name, HP, MP, Lvl, Model)
    setmetatable(newBoss, Boss)
    newBoss.IsDeadly = IsDeadly
    return newBoss
end

--use this instead of default
function Boss:Attack()
    warn("attack unique to this boss")
end

function Boss:IsDeadly()
    warn(self.IsDeadly)
end

return Enemy
#2

This is the way the metatable works

  • You call boss:Attack()
  • boss.Attack doesnt exist so it checks the metatable Boss
  • if it exists it uses it if not it checks the metatable Enemy

So the answer is yes it will overwrite it.

1 Like
#3

Yeah but my question is if I can prevent it from overwriting? I know in Java and other languages you can do that iirc

#4

It won’t overwrite it per se, it will just be the method used for the inherited class. Method calls on the base class will still use the base method. In addition, if you want to use the base method inside of the overwriting method, you can use something like this

function Inheritor:Method(...)
    -- do stuff
    baseClass.Method(self, ...)
end

It’s also a good idea to include a link to the base class in your inheritors.

#5

yeah what @JarodOfOrbiter said, you can have a boss:Attack() and use Enemy:Attack() in it.

[Side Note]: Inheritance can cause you many problems and is generally hated and avoided in favor of composition, you can do a youtube search of “inheritance vs composition” to learn more.
https://www.youtube.com/results?search_query=inheritance+vs+composition

1 Like
How should I go about doing this?
#6

Oh, this might be an issue too. I would alter this to be

local Boss = setmetatable({}, {__index = Enemy})

You shouldn’t notice a difference in your current code, but it will come back to bite you if you ever try to inherit Boss.
Typically when I set up classes (and bear in mind that it’s been a while) I usually start them something like this

local ClassExample = setmetatable({_class = "ClassExample", _base = nil}, {__index = ClassExample})
local InheritanceExample = setmetatable({_class = "InheritanceExample", _base = ClassExample}, {__index = ClassExample})
local SecondInheritor = setmetatable({_class = "SecondInheritor", _base = InheritanceExample}, {__index = InheritanceExample})
#7

Ok so this is a bit random, but after experimenting more I feel like this oop stuff is just useless I’m most likely just doing things wrong, but idk it seems like you can’t even give an inherited class it’s own method without having to make it shared?

I tried adding this to the inherited class

function Boss:Test()
    warn("test")
end

but I just get an error “ServerScriptService.OOPTesting.Script:7: attempt to call a nil value” so I tried doing this

function Enemy:Test()
    warn("test")
end

and now it works however now the enemy class can use that method which I don’t want lol.

#8

I’ve got it working. If this doesn’t help you, can you share the full code as it currently stands which does not work?

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#9

Some will argue OOP is useless, some will argue it’s the greatest thing ever, but almost everyone agrees inheritance is evil and will come back to haunt you when you have a massive hierarchy that’s not easy to change.

Links:
https://neethack.com/2017/04/Why-inheritance-is-bad