How to transfer a luabind::object between two lua states

Question

I store an object by a function call from Lua to C++ in first script in my application and after that I'll try to pass that object to other scripts and vice versa.

A part of script class in C++:

void script::set_property(lua_State* L, luabind::argument const& value)
{
  this->property_field = luabind::object(L, value);
}

luabind::object script::get_property(lua_State* L)
{
  return this->property_field;
}

Then in my script which is Script1.lua I do this:

script1:set_property(a table or a userdata or a string)
print(type(script1:get_property()))

The problem is, values sent by scripts are distinct in different Lua states because every script in my application has its own lua_State. The above code works fine when I call script::get_property from Script1.lua.

Since all of my scripts have access to other scripts in their contexts when I try to do this in other scripts like Script2.lua or Script3.lua or others:

print(type(script1:get_property()))

It won't print data type here properly and it'll return a number instead, which is a wrong result and the reason is script1:get_property() is returning a value that is only understood by script1 and not in other scripts.

I understand values that have been registered in script1 are only registered into that script's stack and registry table particularly and no one else, but my question is, is there any way to transfer these values between different Lua states?

Thanks.

Answer 1

Since you can't guarantee anything about the type of the argument you're passing between the states, essentially what you're looking for is to serialize / de-serialize the object. Fortunately Programming in Lua covers this: Chapter 12 - Data Files and Persistence. Essentially you are converting your Lua object from one state into a stream of bytes, passing it to your C++ layer as a stream of bytes, then passing it to the second state still as a stream of bytes, and then de-serialising it into table/object form again on the other side.

That's the only type-safe, generic way to transfer data of arbitrary types between lua_States, although if you have constraints on the types of data then you might be able to make assumptions about what sort of data you need to serialize.