Annotate as immutable

[Rolln-dev]

Is there any way to make a value immutable? Like treating it as a constant, enum, etc.

So that a warning is triggered if you try to do something like this:

---@enum colors
local COLORS = {
	black = 0,
	red = 2,
	green = 4,
	yellow = 8,
	blue = 16,
	white = 32
}

COLORS.black = 255

Or to be able to mark a class field as constant.

[tomlau10]

I have just found a very hacky way to do so 😂

---@class (exact) colors.*

---@enum colors
local COLORS = {    ---@class colors.*
    black = 0,
    red = 2,
    green = 4,
    yellow = 8,
    blue = 16,
    white = 32
}

COLORS.black = 255  -- warning: inject-field

Explanation (I think it works this way, or is it?) 😂

• @class (exact) means no extra fields can be injected after its definition
  it is usually followed by some @field annotation

---@class (exact) Foo
---@field foo1 integer
---@field foo2 integer
Foo = {}

Foo.foo1 = 1    -- ok
Foo.foo2 = 2    -- ok
Foo.foo3 = 3    -- warn: inject-field

• But in my hack, as no @field are under the @class (exact) colors.* annotation
  => nothing in this class can be redefined
• Then I used a non-exact @class colors.* to annotate the local COLORS
  => this variable now have the type colors.*, along with the initial fields it defined
• You cannot write the (exact) at this line (I tested)
  otherwise the initial fields will also trigger inject-field warnings

[Philofallever]

I think If you really need a readonly table, use metable to do that

[tomlau10]

use metable to do that

I assume you are talking about using metatable and override the __newindex. But that's 2 different things:

• metatable can only check at runtime
• LuaLS can perform static analysis which is way more powerful 😄

[Philofallever]

That sounds pretty, but in my actual work experience, I don't care a table is really readonly. I don't think luals should focus on sloving similar situations

[tomlau10]

I don't think luals should focus on sloving similar situations

You're right, that's why luals seems do not have direct ways to do so (no @const or something like that)
I would say my above example is just a hack 😂 It uses existing annotations, just that they are not originally intended to check readonly