How can I use i++ and ++i from C in Lua

Question

Is there a way to use i++ instead of i = i + 1 in Lua? ~~I think it might be possible since Lua can use C functions directly.~~

`++` is not a C function, it is an operator. So Lua being able to use C functions is not applicable. — Craig S. Anderson, May 09 '15 at 09:36
Possible duplicate of http://stackoverflow.com/questions/7855525/simulate-in-lua-is-it-possible. — lhf, May 09 '15 at 10:27
not necessarily - I'm curious whether there is any hacky way of achieving `i++` in Lua. Thanks anyway. `increment` function is a way around somehow — Mateusz Piotrowski, May 09 '15 at 10:30

score 5 · Answer 1 · answered May 09 '15 at 14:42

You'd have to modify the parser to accept ++, since it's not part of the syntax. Creating a new incompatible dialect of Lua just to save a few characters just isn't worth it, though.

Defining some sort of a function for this won't work in general either, since functions in Lua are pass-by-value, so you'd have to write

i = incr(i)

which pretty much defeats the point, and doesn't let you express ++i anyway.

Maybe you could do incr 'variableName' and mess with the local environment of the calling function... but again, that's just overcomplicated, not worth the trouble and generally a horrible idea in every way imaginable.

score 4 · Accepted Answer · answered May 09 '15 at 18:18

If you want to avoid typing, see if your editor can expand ++i to i = i + 1 for you.

If you just want a hacky way that doesn't involve modifying the Lua source code then tables will get you pass-by-reference and the __call meta-method can be used as an expression or statement.

function num(v)
  local t = {v or 0}
  function postinc(t, i)
    local old = t[1]
    t[1] = t[1] + (i or 1)
    return old
  end
  setmetatable(t, {__call=postinc})
  return t
end


i = num()
print(i())  -- print(i++)
i()         -- i++
print(i(0)) -- print(i)

Writing code like this is never worth it, accessing the "value" of i now requires i(0).

score 2 · Answer 3 · answered Aug 08 '22 at 15:02

2

While you can't do i++ or ++i in Lua by default you can change i = i + 1 to i += 1 which is much better

answered Aug 08 '22 at 15:02

tomsterBG

21
3

"which is much better"—how is it much better? – ChrisGPT was on strike Aug 13 '22 at 02:52

How can I use i++ and ++i from C in Lua

3 Answers3