Lua equivalent for null conditional operator? [duplicate]

Question

In lua, if we try to index a series of nested table (any of which can be nil), we might write code like this:

-- try to get a.b.c

local ret
if a then
    local b = a.b
    if b then
        ret = b.c
    end
end

Which I think is lenthy and ugly. There are also simpler ways:

-- method 1
local ret = a and a.b and a.b.c

-- method 2
local ret = ((a or {}).b or {}).c

I know I'm splitting hairs, but these two methods are still not perfect, method 1 causes more index operations (do a.b twice), method 2 create some unnecessary tables.

So I wonder if there is a way with no side-effect like '?.' in C#? Or '?.' operator violates lua's design philosophy?

Answer 1

Just write a function:

local function nestedIndexOrNil(t, ...)
  for _, k in ipairs{...} do
    if not t then
      return nil
    end
    t = t[k]
  end
  return t
end

nestedIndexOrNil(a, 'b', 'c')