Lua C API - loading multiple files with variables and functions of the same names

user_552613 0
Viewed 732

Say I have two Lua files which I'll be using from the standard Lua C API, that share a common library:

common.lua

function printHello(name)
    print("Hello from " .. name)
end

file1.lua

require "common"
local scriptName = "file1"

function doSomething()
    printHello(scriptName)
end

file2.lua

require "common"
local scriptName = "file2"

function doSomething()
    printHello(scriptName)
end

Now say I want to have both file*.lua files share the same lua_State. Without changing any of the Lua code, how can I load the files in way such that I can call a specific doSomething()?

Is there a way I can move "everything" from the loaded files (functions, variables, tables) it into a global table within the lua_State using the script-name (or whatever) as the key? Also, is there a way I can do this such that file1.lua and file2.lua can share the "in memory" version of common.lua?

I am using Lua 5.1.

Thanks!

embedded-language lua c++
2 Answers

Here's how you do it in pure Lua 5.1:

file1_env = setmetatable({}, {__index = _G})
local file1_chunk = loadfile('file1.lua')
setfenv(file1_chunk, file1_env)
file1_chunk()

file2_env = setmetatable({}, {__index = _G})
local file2_chunk = loadfile('file2.lua')
setfenv(file2_chunk, file2_env)
file2_chunk()

file1_env.doSomething() -- prints "Hello from file1"
file2_env.doSomething() -- prints "Hello from file2"

What's going on is you're changing the environment that each file's chunk runs in, so instead of putting their doSomething functions in the global environment and thus stomping each other, they go in their own local environment (which uses a metatable so they can use things that are in the global environment like require and print). And as requested, common.lua only has to run once, as you'll see if you put something like printHello('common') at the end of it.

If you want to do this from C, all of the functionality I used can be straightforwardly converted to the C API, like this:

#include <lua5.1/lua.h>
#include <lua5.1/lualib.h>
#include <lua5.1/lauxlib.h>

int main(void) {
    lua_State *L = luaL_newstate();
    luaL_openlibs(L);

    /* stack is empty */
    lua_createtable(L, 0, 1);
    /* -1: file1_env */
    lua_createtable(L, 0, 1);
    /* -2: file1_env, -1: file1_env_mt */
    lua_pushvalue(L, LUA_GLOBALSINDEX);
    /* -3: file1_env, -2: file1_env_mt, -1: _G */
    lua_setfield(L, -2, "__index");
    /* -2: file1_env, -1: file1_env_mt */
    lua_setmetatable(L, -2);
    /* -1: file1_env */
    luaL_loadfile(L, "file1.lua");
    /* -2: file1_env, -1: file1_chunk */
    lua_pushvalue(L, -2);
    /* -3: file1_env, -2: file1_chunk, -1: file1_env */
    lua_setfenv(L, -2);
    /* -2: file1_env, -1: file1_chunk */
    lua_call(L, 0, 0);
    /* -1: file1_env */
    lua_setglobal(L, "file1_env");
    /* stack is empty */
    lua_createtable(L, 0, 1);
    /* -1: file2_env */
    lua_createtable(L, 0, 1);
    /* -2: file2_env, -1: file2_env_mt */
    lua_pushvalue(L, LUA_GLOBALSINDEX);
    /* -3: file2_env, -2: file2_env_mt, -1: _G */
    lua_setfield(L, -2, "__index");
    /* -2: file2_env, -1: file2_env_mt */
    lua_setmetatable(L, -2);
    /* -1: file2_env */
    luaL_loadfile(L, "file2.lua");
    /* -2: file2_env, -1: file2_chunk */
    lua_pushvalue(L, -2);
    /* -3: file2_env, -2: file2_chunk, -1: file2_env */
    lua_setfenv(L, -2);
    /* -2: file2_env, -1: file2_chunk */
    lua_call(L, 0, 0);
    /* -1: file2_env */
    lua_setglobal(L, "file2_env");
    /* stack is empty */
    lua_getglobal(L, "file1_env");
    /* -1: file1_env */
    lua_getfield(L, -1, "doSomething");
    /* -2: file1_env, -1: file1_env.doSomething */
    lua_call(L, 0, 0);
    /* -1: file1_env */
    lua_pop(L, 1);
    /* stack is empty */
    lua_getglobal(L, "file2_env");
    /* -1: file2_env */
    lua_getfield(L, -1, "doSomething");
    /* -2: file2_env, -1: file2_env.doSomething */
    lua_call(L, 0, 0);
    /* -1: file2_env */
    lua_pop(L, 1);
    /* stack is empty */

    lua_close(L);
    return 0;
}
user_75090650

FYI, the above answer no longer works with the latest versions of LUA. Specifically,

lua_pushvalue(L, LUA_GLOBALSINDEX);

and

lua_setfenv(L, -2);

are no longer supported. Because I am a LUA neophyte, I do not know what equivalent LUA api calls should be used as replacements. If someone could update that answer to work with LUA 5.4, it would be much appreciated. I apologize that I failed to follow protocol for not commenting directly in the answer, but I apparently don't have sufficient reputation to do so.

user_42560060
Related