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#Crystal

Crystal is a lightweight framework for Roblox that simplifies communication between core parts of your game and seamlessly bridges the gap between the server and the client.

Install

Installing Crystal is very simple. Just drop the module into ReplicatedStorage. Roblox Studio workflow:

1. Get Crystal from the Release.
2. Place Crystal directly within ReplicatedStorage.

Basic Usage

The core usage of Crystal is the same from the server and the client. The general pattern is to create a single script on the server and a single script on the client. These scripts will load Crystal, create services/controllers, and then start Crystal.

The most basic usage would look as such:

local Crystal = require(game:GetService("ReplicatedStorage").Packages.Crystal)

Crystal.Start():catch(warn)
-- Crystal.Start() returns a Promise, so we are catching any errors and feeding it to the built-in 'warn' function
-- You could also chain 'await()' to the end to yield until the whole sequence is completed:
--    Crystal.Start():catch(warn):await()

That would be the necessary code on both the server and the client. However, nothing interesting is going to happen. Let's dive into some more examples.

A Simple Service

A service is simply a structure that serves some specific purpose. For instance, a game might have a MoneyService, which manages in-game currency for players. Let's look at a simple example:

local Crystal = require(game:GetService("ReplicatedStorage").Packages.Crystal)

-- Create the service:
local MoneyService = Crystal.CreateService {
	Name = "MoneyService",
}

-- Add some methods to the service:

function MoneyService:GetMoney(player)
	-- Do some sort of data fetch
	local money = someDataStore:GetAsync("money")
	return money
end

function MoneyService:GiveMoney(player, amount)
	-- Do some sort of data fetch
	local money = self:GetMoney(player)
	money += amount
	someDataStore:SetAsync("money", money)
end

Crystal.Start():catch(warn)

Now we have a little MoneyService that can get and give money to a player. However, only the server can use this at the moment. What if we want clients to fetch how much money they have? To do this, we have to create some client-side code to consume our service. We could create a controller, but it's not necessary for this example.

First, we need to expose a method to the client. We can do this by writing methods on the service's Client table:

-- Money service on the server
...
function MoneyService.Client:GetMoney(player)
	-- We already wrote this method, so we can just call the other one.
	-- 'self.Server' will reference back to the root MoneyService.
	return self.Server:GetMoney(player)
end
...

We can write client-side code to fetch money from the service:

-- Client-side code
local Crystal = require(game:GetService("ReplicatedStorage").Packages.Crystal)
Crystal.Start():catch(warn):await()

local MoneyService = Crystal.GetService("MoneyService")

MoneyService:GetMoney():andThen(function(money)
	print(money)
end)

Under the hood, Crystal is creating a RemoteFunction bound to the service's GetMoney method. Crystal keeps RemoteFunctions and RemoteEvents out of the way so that developers can focus on writing code and not building networking infrastructure.