Making number and integer classes (partial)

[Polanas]

I wanted to make a PR for this, but it's probably better to ask first to avoid potential time waste.
Can number and integer classes be made partial? This is really useful for defining methods on numbers.
For example, having a metatable on them with __index containing math functions, one can write

---@class (partial) number
---@field sin fun(self: number): number
--- ...

--evaluates to number
local x = x:sin():abs():round()

instead of

local x = math.round(math.abs(math.sin(x)))

[CppCXY]

It doesn't make sense. We directly assume that number types are POD types in the code, and the definitions in builtin are only for code completion.

[Polanas]

That's unfortunate :(
Strings are also plain data types, yet this works perfectly:

---@param self string
string.print = function(self)
  print(self)
end

--print is type checked
("idk"):print()

[Polanas]

and the definitions in builtin are only for code completion.

Yes, of course! Im not suggesting to define anything in there. Simply making the class partial would allow users to define their own functions/methods on numbers.

[CppCXY]

In Lua, numbers do not have a metatable, while strings do. Moreover, extending strings is a common practice. When we encounter the string type, we directly look up fields in the string table.

[Polanas]

When we encounter the string type, we directly look up fields in the string table.

Ah, so numbers are treated differently, I see. Yeah, then it's not as straightforward as I thought.

In Lua, numbers do not have a metatable, while strings do

By default they do not, but there is nothing stopping one from setting it :D
mlua, for example, provides this api
It's available in all supported lua versions, including luajit and luau. It's implemented as

lua_push[number/string/etc](...);
lua_setmetatable(...);

using the C api.

To be honest I'm surprised this isn't really mentioned much. Depending on the application it can be really powerful. For this reason I believe making number (and ideally function too) (partial) brings some value.