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Have you noticed how nil is a separate type, and any form of typechecking...:

    local function f(x)
      assert(type(x) == "table")

... is non-nil by default?

    assert(pcall(f, nil) == false)

Of course, lua can only typecheck at runtime. But here's an example:

    local function f(x)
      --assert(type(x) == "function")
      return {dothing=x}

    local v = f(nil)


When running this code, you get an error on line "v:dothing()". If you uncomment the assertion, you get an error on line "local v = f(nil)" instead, which is much more helpful.

This is why I made typecheck[1].


Side-note: For some reason most static type checking (e.g. C) is nullable-by-default, while most dynamic/runtime type checking (e.g. Lua) is non-null-by-default. And Java has both (`null instanceof Something` is always false, yet you can pass `null` to a method expecting a `Something` without any warnings).

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