Support generic table

[ibachar]

Hi,

Is it possible to create a generic table such that the returned type is the key as a type. For example:

---@class MyClass
local MyClass = {}

---@generic T
---@type table<'T', T>
local Classes = {}

local c = Classes["MyClass"]

In the above example, I expect c to have the type MyClass

[tomlau10]

Is it possible to create a generic table such that the returned type is the key as a type.

is this a feature request?

If this is just a question, then I don't think it's possible. 🤔
The closest I can think of, is to use a function to capture the literal string, and return it as the type

---@class MyClass
local MyClass = {}

local Classes = {}

---@generic T
---@param className `T`
---@return T
function GetClass(className)
    return Classes[className]
end

local c = GetClass("MyClass") --> c: MyClass

• the backtick means capture the input string as a type: https://luals.github.io/wiki/annotations/#generic
  (the Capture with Backticks example)
• however this require a changes of syntax in your code, so this might not satisfy your requirement

---

ps:
for questions / q&a, please consider using the discussion: https://github.com/LuaLS/lua-language-server/discussions
issue page is for tracking bugs / incorrect behavior / etc. 😅

but if this is a feature request, then you may keep it open.
Though I don't think maintainers will have time to finish it, given that it has workarounds/alternatives, and not a serious bug either.

[CppCXY]

I suggest you look this: #3017

[tomlau10]

I suggest you look this: #3017

I think this is different from what requested in this issue 😕

• The author wants
  • Classes["MyClass"] => return MyClass
  • Classes["YourClass"] => return YourClass
• But not a generic class that always return the template type
  • The example given in your reply is that MyClass<string> => every string index to it returns a string value

[CppCXY]

I think this is different from what requested in this issue 😕

• The author wants

  • Classes["MyClass"] => return MyClass
  • Classes["YourClass"] => return YourClass

• But not a generic class that always return the template type

  • The example given in your reply is that MyClass<string> => every string index to it returns a string value

Ok, I have namespace type:

However, I don't have a global namespace. Adding this is not difficult.

[ibachar]

@tomlau10 Yes this is a feature request. For now I've implemented it using a predefined set of types in the table

[tomlau10]

For now I've implemented it using a predefined set of types in the table

Yeah~ I almost forget that you can have a class and define the fields of it.
But as you might guess, need to update it every time you add a new class, so quite troublesome 🙁

---@class MyClass
local MyClass = {}

---@class YourClass
local YourClass = {}

---@class Classes
---@field MyClass MyClass
---@field YourClass YourClass
local Classes = {}

local c1 = Classes["MyClass"]   --> c1: MyClass
local c2 = Classes["YourClass"] --> c2: YourClass
local c3 = Classes["HisClass"]  --> c3: unknown

An improved version

luals supports C# partial class define style.
You can add @field to the same class in different parts of your code, so no need to write them all at once.
=> you can break up those @class definition

• Classes.lua

---@class Classes
local Classes = {}

return Classes

• MyClass.lua

---@class MyClass
local MyClass = {}

---@class Classes
---@field MyClass MyClass
-- luals now knows `Classes.MyClass` = MyClass type

return MyClass

• YourClass.lua

---@class YourClass
local YourClass = {}

---@class Classes
---@field YourClass YourClass
-- luals now knows `Classes.YourClass` = YourClass type as well

return YourClass

• main.lua

local Classes = require "Classes"

local c1 = Classes["MyClass"]   --> c1: MyClass
local c2 = Classes["YourClass"] --> c2: YourClass
local c3 = Classes["HisClass"]  --> c3: unknown

---

These workarounds might suit your need before this feature request is implemented.
Also maybe you would like to try CppCXY's language server, it has much better generic support. 😄