flodihn
Hello, I chose to use Elixir as “scripting” language for my game, I am very new to Elixir but I know Erlang well.
My goal is to somewhat replicate LPC, which is an object oriented langage in C for LP Muds which used a lot back in the days.
So far I managed to come by borrowing examples from an OOP lib I found here: oop/lib/oop.ex at master · wojtekmach/oop · GitHub
What I want to do is to define game objects, and let them “inherit” from a parent object, like this:
Ao.ShortSword -> Ao.Weapon -> Ao.Object
This is done by defining an object macro that lets me inherit from one other object with the :: expression, for example Ao.Weapon :: Ao.Object
If the object macro detects the precense of an inherited object, it will create delegates for all methods in the parent and delegate from the object to the parent.
So far everything works like a charm, but now I need to add “properties” to the objects. A property is a key,value that describes the object some how, for example:
set_property(:colors, [{:red, 80, :yellow, 20}])
set_property(:materials: [{:bronze, 100}])
set_property(:mesh, <<"BronzeShortSword.fbx">>)
The issue I am trying to solve now that not all properties are equal, they are divided into shallow and deep properties. Shallow properties are things that I expect
to be queried more than 99.99% of the times, in most cases this would be properties like:
:position
:rotation
:mesh
These would be saved in a mnesia table for quick access.
And then all other properties that will only be queried or written in rare cases are saved in a long term (slower) database, such as Riak.
To define this I thought I could use Elixirs built-in attribute system, for example:
object Ao.Weapon :: Ao.Object do
@shallow :position
@shallow :rotation
@shallow :mesh
The problem I face is that the Ao.Object.set_property needs to know the objects (Ao.Weapon) shallow attributes so it can store the value in the mnesia DB
instead of Riak, but can not access it because they are stored in Ao.Weapon.
Right now I am considering defining the set_property function in a macro when creating the module using the object macro, but to be honest, I have literally no idea what is a good approach for this.
I hope that someone can guide me towards a good solution.
Here is the code I have so far, please note at Code.eval_quoted(method, [], __ENV__) I add the delegate, maybe a good solution would be to pass the module Ao.Weapon to the Ao.Object.set_property there:
defmodule Ao do
defmacro object(obj_expr, block, _opts \\ []) do
{object, parent} = case obj_expr do
{:"::", _, [obj, parent]} ->
{obj, parent}
obj ->
{obj, nil}
end
AoLibObj.Builder.build(object, parent, block)
end
end
defmodule AoLibObj.Builder do
def build(object, parent, block) do
quote do
defmodule unquote(object) do
parent_obj = unquote(parent)
Module.register_attribute(__MODULE__, :parent, accumulate: false)
Module.put_attribute(__MODULE__, :parent, parent_obj)
Module.register_attribute(__MODULE__, :shallow, accumulate: true)
unquote(block)
def methods do
built_ins = [
object: 0, methods: 0, clone: 1
]
__MODULE__.__info__(:functions) -- built_ins
end
if parent_obj != nil do
for {fun, arity} <- parent_obj.methods() do
method = AoLibObj.Builder.inherit_method(fun, arity, parent_obj)
Code.eval_quoted(method, [], __ENV__)
IO.inspect(fun)
end
end
def clone(uid \\ nil) do
uid = if uid == nil do AoLibObj.Builder.make_uid() else uid end
%{
:uid => uid,
:object => unquote(object),
}
end
end
end
end
def inherit_method(method, arity, parent_obj) do
args = (0..arity) |> Enum.drop(1) |> Enum.map(fn i -> {:"arg#{i}", [], Ao} end)
IO.inspect(args)
{:defdelegate, [context: Ao, import: Kernel],
[{method, [], args}, [to: parent_obj]]}
end
def make_uid() do
<<a::32, b::16, c::16, d::16, e::48>> = :crypto.strong_rand_bytes(16)
str =
:io_lib.format(
"~8.16.0b-~4.16.0b-4~3.16.0b-~4.16.0b-~12.16.0b",
[a, b, Bitwise.band(4095, c), Bitwise.band(16383, d), Bitwise.bor(32768, e)]
)
:erlang.list_to_binary(str)
end
end
import Ao
object Ao.Object do
def init() do
IO.puts("Instanced Ao.Object!")
end
def set_property(_key, _value, child \\ nil ) do
IO.puts("BASE!!! Ao.Object")
end
end
import Ao
object Ao.Weapon :: Ao.Object do
@shallow :position
@shallow :rotation
@shallow :mesh
end
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First 4 of 4 Posts
stevensonmt
I hope someone with more experience chimes in, but I think it is important to recognize that trying to shoe-horn object oriented paradigms like inheritance is destined to fall short in Elixir. Inheritance just is not part of the language by design.
I would recommend you define behaviours for your “object classes” and then have each specific module implement the behaviours it requires. So a sword can implement weapon behaviour, and a shovel can implement weapon behaviour and tool behaviour and so on.
benwilson512
Hey @flodihn, sounds like an interesting space! As @stevensonmt says though, this:
is not a strategy that I think will lead you to success. You should re-envision your requirements to match a functional language, or pick a scripting language with objects and inheritance built in. Attempting to shoehorn it into Elixir is going to be both very difficult and also very lonely, because there really aren’t other people in the ecosystem attempting to do it.
EDIT: I suppose a third, sort of “out there” answer would be to implement an LPC runtime in Elixir such that you could just straight up use LPC as your game scripting language. This is by no means the most efficient use of time, but could be a lot of fun!
kokolegorille
You could use luerl, lua on the BEAM.
There is a spaceship game demo by @rvirding and videos on YT about luerl.
andyleclair
You should actually watch the youtube video linked in the OOP repo.
It is not serious, and you should not take it as a good example.
If you want an Entity Component System, you may want to try GitHub - ecsx-framework/ECSx: An Entity-Component-System framework for Elixir · GitHub