Function whose return type is supplied as parameter

[EvanBalster]

Hello! I'm making a game engine that makes pervasive use of methods like room:contents(Creature). The contents method returns all objects that inherit from the type passed to the method. Therefore the return type equals the value of the first parameter.

My first attempt:

---@param select_type table   Aspect type.
---@return select_type[]
function Domain:contents(select_type) ...

My second:

---@generic T
---@param select_type `T`   Aspect type.
---@return T[]
function Domain:contents(select_type) ...

With the second implementation, room:contents(Creature)[1] is reported as type <T> rather than being of type Creature or the base class of Creature. Type information is lost and autocomplete does not produce any useful info.

[EvanBalster]

Wouldn't you know it, I figured it out right after opening the question. The 'capturing' backticks are unnecessary and removing them makes the function work as expected:

---@generic T
---@param select_type T  Aspect type.
---@return T[]
function Domain:contents(select_type) ...

room:contents(Creature) now returns Creature[] as expected.

[tomlau10]

The backtick capture annotation `T` is for capturing a literal string param and convert it into a class. See the example Capture with Backticks in the wiki: https://luals.github.io/wiki/annotations/#generic

And yes, in your case you don't need the backtick 👍

[ChrisKader]

I wish we could use the same notation to reference class fields or even literals in the environment. So something like

---@class Test
---@field Field Class2
local Test = {}

_G.test = 1

---@generic F
---@param field `F`
---@return _G[F] | _G<F> | Test[F] | Test<F>
function thisTest(field)

end

local z = thisTest("test")
z == _G.test

local y = thisTest("Field")

y == Test.Field