The evergreen way to describe Roblox instance trees and validate instances with.

Why Tree?

In game development, particularly Roblox, it's crucial to verify that incoming instances adheres to a specific structure. For instance, in genres like JToH-esque towers and flood escape, kits must conform to a set structure to function correctly. For example, games like Tria.OS allows playtesting of user-created maps, but only if they comply with a given structure.

Tree aims to simplify this by allowing you to declaratively describe an instance tree, returning a describer function to check instances against.

It's better if you see it in practice:

-- Without Tree
local function validate(instance: Instance): boolean
    local client_objects = instance:FindFirstChild("ClientObjectScripts")
    local obby = instance:FindFirstChild("Obby")
    local frame = instance:FindFirstChild("Frame")

    return instance.ClassName == "Folder"
        and client_objects
        and client_objects.ClassName == "Folder"
        and obby
        and obby.ClassName == "Folder"
        and frame
        and frame.ClassName == "Model"
end

-- With Tree
local validate = Tree.describe {
    class_name = "Folder",
    children = {
        ClientObjectScripts = Tree.class_of("Folder"),
        Obby = Tree.class_of("Folder"),
        Frame = Tree.class_of("Model")
    }
}

-- Tree provides a helpful error message if the description fails
local ok, reason = validate(data.TowerObj)
if not ok then
    return warn("Failed to get tower;", reason)
else
    return print("Got tower!")
end

Installation

Install via Roblox

Tree can be installed as a Roblox model. Simply grab the latest release from the release page.

Install via Wally

Tree can be installed through Wally, simply append this to your wally.toml file:

[dependencies]
tree = "znotfireman/[email protected]"

Install via Source

Tree is distribued as a single module. Thus, you can install it by obtaining its source code to a new Tree.luau file.

API

type Describer = (Instance: instance?) -> (boolean, string?)

A function that, given an instance, validates that it matches an instance tree description. Returns if the instance matches the description, and an error message if it fails.

function Tree.new(description: {
    class_name: string?,
    is_a: string?,

    properties: { [string]: any }?,
    children: { [string]: Describer }?,
    attributes: { [string]: any }?,
}): Describer

Constructs and returns a new describer given an instance description:

• If class_name is specified, validates that the class name of the instance exactly matches the given class name. Internally compares both class names.
• If is_a is specified, validates that the instance inherits from the given class name. Internally calls :IsA() with the given class name.
• If properties is specified, every property provided will be checked against the instance with the expected value.
• If children is specified, every child provided will have its describer checked with the instance's real child.
• If attributes is specified, every attribute provided will be checked against the instance with the expected value.

function Tree.class_of(class_name: string): Describer

Constructs and returns a new describer that matches an instance which is the exact provided class name.

function Tree.which_is_a(class_name: string): Describer

Constructs and returns a new describer that matches an instance which inherits from the provided class name.

function Tree.optional(inner_describer: Describer): Describer

Constructs and returns a new describer that allows nil instances. If such an instance exists, it is ran through the provided inner describer.

License

MIT License

Copyright (c) 2024 znotfireman

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.