Strategy to deal with middleclass statics?

[jtackaberry]

#1172 offers an approach to work with middleclass's class initialization:

local class = require('middleclass')

--- @class Foo
--- @overload fun():Foo
Foo = class('Foo')

local f = Foo()

One of middleclass's features is to set a static values under a static table, after which point those values are accessible from the class:

--- @class Foo
--- @overload fun():Foo
Foo = class('Foo')
Foo.static.bar = 42

-- This prints 42
print(Foo.bar)

Unfortunately #1172 didn't address that aspect of the user's question, presumably because handling typing here is problematic.

I can get a bit further by declaring the static field on the class via @field:

--- @class Foo
--- @field static table<string, any>
--- @overload fun():Foo
Foo = class('Foo')

--- @type integer
Foo.static.bar = 42

-- This prints 42, but LuaLS flags it as an undefined field.
print(Foo.bar)

The only way I can see is to predefine all static values as @field below the @class:

--- @class Foo
--- @field static table<string, any>
--- @field bar integer
--- @overload fun():Foo
Foo = class('Foo')

Foo.static.bar = 42

-- This prints 42
print(Foo.bar)

This suppresses the undefined field warning and the type of Foo.bar is now known, but it's not ideal: when jumping to the definition of Foo.bar it of course lands on the @field line rather than the Foo.static.bar assignment.

Is there a better way to approach this?

[gphg]

Nah. Looks lot of works. I have a better approach.

Check out the annotation definition I often use:

---@meta


---kikito middleclass instance definition
---@class instance<string, any>
---
---@field class class
---
---@field initialize fun(self: self, ...)
---@field isInstanceOf fun(self: self, other: class|table): boolean


---kikito middleclass class definition
---@class class: instance
---@overload fun(): instance
---
---@field name string
---@field super class?
---@field static self
---
---@field protected __instanceDict instance
---@field protected __declaredMethods table<string, function>
---@field subclasses { [self]: true }
---@field allocate fun(self: self): instance
---@field new fun(self: self): instance
---@field subclass fun(self: self, newSublassName: string): aNewSubclass: self
---@field subclassed fun(self: self, other: self|table)
---@field isSubclassOf fun(self: self, other: self|table): boolean
---@field include fun(self: self, ...): self

Then overload the context of loaded middleclass package, on required. Usually once.

---@module 'middleclass'
---@overload fun(className: string, super?: table): class
local middleclass = require('src.libraries.middleclass.middleclass')

---Aliasing 'middleclass.middleclass' into 'middleclass', incase it is required by other libraries.
if package.loaded['middleclass'] ~= middleclass then
	package.loaded['middleclass'] = middleclass
end

Let's say, I have to define a Superclass for all my project's classes named Object.

local weakKeys, weakValues = { __mode = 'k' }, { __mode = 'v' }
local NOOP = function() end
local _initializedInstances = setmetatable({}, weakKeys) ---@type { [Object]: true? }

---Lua reimplementation of https://love2d.org/wiki/Object
---@class ObjectClass: Object, class
---@overload fun(): Object
---@field new fun(): Object
---@field static self
local ObjectClass = require 'middleclass' ('game.Object')

---Define class's statics and also redefine the class itself.
---@class ObjectClass
local staticObjectClass = ObjectClass.static

staticObjectClass._VERSION = '0.0.1-TRY-0'

---@param logger? function|true
---@return table
function staticObjectClass:debugInfoGetAllInstance(logger)
	logger = logger == true and print
		or type(logger) == 'function' and logger
		or NOOP
	local t = setmetatable({}, weakValues) -- return a weaktable
	for o in pairs(_initializedInstances) do
		table.insert(t, o)
		logger(#t, o)
	end
	return t
end

---@return boolean success # `true` if the object was initialized by this call, `false` if it had been previously initialized (prevent from being re-initialized).
function ObjectClass:initialize()
	if _initializedInstances[self] then return false end
	--> BEGIN
	-- some initialization goes here
	--> END
	_initializedInstances[self] = true
	return true
end

---@class Object: instance
local Object = {}

---@return boolean success # `true` if the object was released by this call, `false` if it had been previously released.
function Object:release()
	if not _initializedInstances[self] then return true end
	_initializedInstances[self] = nil
	return false
end

function Object:type()
  return self.class and self.class.name or type(self)
end

function Object:typeOf(name)
  -- TODO: this checkout class name of current object TIL last super.
end

-- include last
ObjectClass:include(Object)

return ObjectClass

From code above, take a look at these line:

---@class ObjectClass
local staticObject = ObjectClass.static

---@param logger? function|true
---@return table
function staticObject:debugInfoGetAllInstance(logger)
   -- ...omitted...
end

That is how I define a class static.

[gphg]

Class highlight:

Initiated Object highlight:

You might notice that class has initialize method. This method is available on both class and object. I have to put some logic to prevent it reset itself as this method get called. It means ob1:initialize() does nothing.

[jkopano]

When trying to overload constructor like so:

---@class Entity.Class: Entity, class
---@overload fun(O: table): Entity -- without this line i do not get warning
local EntityClass = class("Entity")

i get following warning:

Diagnostics:
1. Cannot assign `class` to `Entity.Class`.
   - `class` cannot match `Entity.Class`
   - Type `class` cannot match `Entity.Class`
   - Type `instance` cannot match `Entity.Class`
   - Type `class` cannot match `unknown`
   - Type `instance` cannot match `unknown` [assign-type-mismatch]

[tomlau10]

When trying to overload constructor like so:
i get following warning:

I believe this is related to #2978, and I have a proposed fix there: #2978 (comment).
Unfortunately no one tested it so no PR so far.

The current workaround is enabling type.weakUnionCheck setting, as explained here: #2978 (comment)

@Mugworth