Symbol class usage?

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1

Hello. I’ve been trying to understand knit framework’s source code. and I’ve found this module called “Symbol” and I wonder what it’s use case?

Here is the symbol module

-- Symbol
-- Stephen Leitnick
-- December 27, 2020

--[[

	symbol = Symbol.new(id: string [, scope: Symbol])

	Symbol.Is(obj: any): boolean
	Symbol.IsInScope(obj: any, scope: Symbol): boolean

--]]


local CLASSNAME = "Symbol"

local Symbol = {}
Symbol.__index = Symbol


function Symbol.new(id, scope)
	assert(id ~= nil, "Symbol ID cannot be nil")
	if (scope ~= nil) then
		assert(Symbol.Is(scope), "Scope must be a Symbol or nil")
	end
	local self = setmetatable({
		ClassName = CLASSNAME;
		_id = id;
		_scope = scope;
	}, Symbol)
	return self
end


function Symbol.Is(obj)
	return (type(obj) == "table" and getmetatable(obj) == Symbol)
end


function Symbol.IsInScope(obj, scope)
	return (Symbol.Is(obj) and obj._scope == scope)
end


function Symbol:__tostring()
	return ("Symbol<%s>"):format(self._id)
end


return Symbol

and here is a module that I found using it

-- EnumList
-- Stephen Leitnick
-- January 08, 2021

--[[

	enumList = EnumList.new(name: string, enums: string[])

	enumList:Is(item)


	Example:

		direction = EnumList.new("Direction", {"Up", "Down", "Left", "Right"})
		leftDir = direction.Left
		print("IsDirection", direction:Is(leftDir))

--]]


local Symbol = require(script.Parent.Symbol)

local EnumList = {}


function EnumList.new(name, enums)
	local scope = Symbol.new(name)
	local enumItems = {}
	for _,enumName in ipairs(enums) do
		enumItems[enumName] = Symbol.new(enumName, scope)
	end
	local self = setmetatable({
		_scope = scope;
	}, {
		__index = function(_t, k)
			if (enumItems[k]) then
				return enumItems[k]
			elseif (EnumList[k]) then
				return EnumList[k]
			else
				error("Unknown " .. name .. ": " .. tostring(k), 2)
			end
		end;
		__newindex = function()
			error("Cannot add new " .. name, 2)
		end;
	})
	return self
end


function EnumList:Is(obj)
	return Symbol.IsInScope(obj, self._scope)
end


return EnumList