Class self bindings not preserved through destructuring of methods

[Agapurnis]

Alternatively: Destructing a class method causes it to lose it's sense of self ;)

I'm not entirely sure how one would go about fixing this, but I'd figure I may as well report it instead of letting it go undocumented.

One potential way might be to simply pass the _binding with all invocations.

-- ...
local _binding = messenger
local sayHi = _binding.sayHi
sayHi(_binding)
-- ...

Or treat it as an alias during compilation, not creating a separate variable.

---

• https://roblox-ts.com/playground/#code/MYGwhgzhAECyCmV4DsDm8BO0DeAoAkALaIRjrQC80ARABLwggD2ANNAO5MYgAmAhNQDcuAqQCetAJbQAFAEocBfAAcMk5ABcZGgBaSIAOmJQy8OcPwBfXNdzAmyCBujGIKdFirJ47OCXeY8sK4rgEYBuJSQdAA9DHQACp6MJwYANYwAGbq8AYi9o7O2NCR0paULv5omMGl0XHQAJJQAK7w0GBqbjA6mLkiQA
• https://luau-lang.org/demo

Input:

class Messenger {
	message = "Hello, world!";

	sayHi () {
		print(this.message);
	}
}

const messenger = new Messenger();

messenger.sayHi(); // This works fine.

const { sayHi } = messenger;

sayHi(); // Issue arises here.

A more realistic case where one might encounter would likely involve destructuring in callback parameters, which is where I found encountered this issue.

Output:

-- Compiled with roblox-ts v1.3.3
local Messenger
do
	Messenger = setmetatable({}, {
		__tostring = function()
			return "Messenger"
		end,
	})
	Messenger.__index = Messenger
	function Messenger.new(...)
		local self = setmetatable({}, Messenger)
		return self:constructor(...) or self
	end
	function Messenger:constructor()
		self.message = "Hello, world!"
	end
	function Messenger:sayHi()
		print(self.message)
	end
end
local messenger = Messenger.new()
messenger:sayHi()
local _binding = messenger
local sayHi = _binding.sayHi
sayHi()
return nil

Error:

8: attempt to index nil with 'message'

[Dionysusnu]

Pretty sure I've already got this fixed in a PR - or maybe even merged into master already.

Yes, fixed by #1888 which is already merged. That should work with classes too, but I'll double check later just to make sure.

[Validark]

For now, this is an intentional design limitation of TS. See microsoft/TypeScript#35451 & microsoft/TypeScript#44513 & microsoft/TypeScript#33201. You can opt-in to having this behavior checked by making the first parameter of your methods be this: this.

https://roblox-ts.com/playground/#code/MYGwhgzhAECyCmV4DsDm8BO0DeAoAkALaIRjrQC80ARABLwggD2ANNAO5MYgAmAhNQDcuAqQCetAJbQAFABcAFpIgAuaIuUBKHAXwAHDJORz5SiADpiUMvE3D8AX1xPcwJsghzoViCnRYqZHh2OBI-TBk7ER9wjHNxKUjBaAB6FOgAFTMOLgBrGAAzI3hzETcPL2xoBOkHSm8wtExhXBqk1PSASSgAV3hoMENfGAVMEpEgA