Question

In the following Lua code:

function eq_event(op1, op2)
    if op1 == op2 then
        return true
    end
    local h = getequalhandler(op1, op2)
    if h then
        return not not h(op1, op2)
    else
        return false
    end
end

why use not not before the return value? is it different with the raw return value? I also remember that in C, there also got chance to use the !! before some expression, does them the same?

Answer 1

not not will convert nil into false, and all other values except false to true. You may need to return a boolean value only when interacting with C.

Yes it’s the same as !! in C. Only difference is that in C, 0 (and some other values I don’t remember) is also falsy (that is, they’ll return false when doubled not’d).