`new_handle` / `from_handle` example script

handle.cpp

// compile with g++ -fpic -shared handle.cpp -o libhandle.so
#include <cstdint>

extern "C" {
    using LuaHandle = uint64_t;
    LuaHandle maybe(LuaHandle h, bool ret) {
        if (ret) return h;
        return 0;
    }
}

test.lua

local ffi = require 'ffi'
ffi.cdef [[
   uint64_t maybe(uint64_t handle, bool ret);
]]
local hlib = ffi.load("./libhandle.so")
local io = require 'io'

local res = {}
local res_cnt = 0

jit.opt.start("hotloop=10")

local holder = {}
local holder_cnt = 0

for i=1, 100 do
   holder_cnt = holder_cnt + 1
   holder[holder_cnt] = { a = i}
   local handle = ffi.new_handle(holder[holder_cnt])
   local ret = hlib.maybe(handle, i % 2 == 0)

   if ret ~= 0 then
      assert(i % 2 == 0)
      res_cnt = res_cnt + 1
      res[res_cnt] = ffi.from_handle(ret)
   else
      assert(i % 2 ~= 0)
   end
end

print("Total of " .. #res .. " results")
for i = 1, #res do
   if type(res[i]) == "table" then
      print("res[" .. i .. "] = table element " .. res[i].a .. ".")
   else
      print("res[" .. i .. "] = number " .. res[i] .. ".")
   end

end