... parameter annotation

[ayhon]

We can use EmmyLua annotations to give a type to the parameters of a function

---@param n number
function fact(n)
  return n == 0 and 1 or n*fact(n-1)
end

However, in some functions we may have an ellipsis (...) which indicates that a variable number of parameters can be used. The way this has come up in a personal project of mine is with a generic Tree constructor, which assumes any extra arguments are children subtress of the tree constructed.

---@class Tree

---@param x any
---@param ... Tree[]
function Tree:new(x, ...)
  local obj = {
    value = x,
    children = {...},
    parent = nil,
    depth = 0
  }
  self.__index = self
  return setmetatable(obj, self)

However, addressing ... in the annotation doesn't seem to work, as I get a <param name> expected. error.

I've tried ... and {...}, but neither seem to work. I looked at the official EmmyLua annotations website, and it seems like this use case was not considered.

I was wondering if there was a way to cover my use case, and if not, to propose using {...}, as it forms an object for which we do have an annotation. (Since ... Tree[] is technically wrong, while {...} Tree[] isn't)

[lua-rocks]

Don't you read the documentation? "..." is called vararg:

@vararg

Indicates a function has multiple variable arguments.

---@vararg string
---@return string
function strconcat(...) end

For returning a vararg you can use ... as a type.

---@vararg string
---@return ...
function tostringall(...) end