Bind an Objective-C object to an existent Lua variable

Question

I have to bind an Objective-C object to a variable of a Lua script. I don't have write access to this Lua script, I just load and run it from the Objective-C code. I know it uses a variable, called luaVar, that uses methods defined in the object. Here is the Lua code:

function run()
    print("Running Lua script")
    print(luaVar)
    print("Ending Lua script")
end

run()

This script should print the luaVar variable, and not nil. Now, here is the Objective-C code I use. The function validate gets the Lua code in the script variable and the object to pass to Lua as f in the theObject variable:

#import "ScriptObject.h"

static const char* SCRIPT_OBJECT_LUA_KEY = "f";
ScriptObject* scriptObject = nil;

- (void)validate:(NSString*)script withObject:(ScriptObject*)theObject {

    L = luaL_newstate(); // create a new state structure for the interpreter
    luaL_openlibs(L); // load all the standard libraries into the interpreter
    lua_settop(L, 0);
    newScriptObject(L);

    // load the script
    int err = luaL_loadstring(L, [script cStringUsingEncoding:NSASCIIStringEncoding]);
    if (LUA_OK != err) {
        NSLog(@"Error while loading Lua script!");
        lua_pop(L, 1);
        return NO;
    }

    // call the script
    err = lua_pcall(L, 0, LUA_MULTRET, 0);
    if (LUA_OK != err) {
        NSLog(@"Error while running Lua script: %s", lua_tostring(L, -1));
        lua_pop(L, 1);
        return NO;
    }

    lua_close(L);
}


static int newScriptObject(lua_State *L) {
    ScriptObject * __strong *lgo = (ScriptObject * __strong *)lua_newuserdata(L, sizeof(ScriptObject *));
    *lgo = scriptObject;

    luaL_getmetatable(L, SCRIPT_OBJECT_LUA_KEY);
    lua_setmetatable(L, -2);

    lua_newtable(L);
    lua_setuservalue(L, -2);

    NSLog(@"New ScriptObject created");
    return 1;

}

I tried the approach from this SO answer, but that didn't handle Objective-C objects. I looked at this question, but it is not clear how it does the binding.

Does anyone know how to do that?

What do you want to do with the object? What does "it uses methods defined in the object" mean? — , Jan 14 '14 at 11:59
@H2CO3 I want to call some of its methods. For example, if the Objective-C object has a `(NSString*)getString()` method, the Lua code may call `luaVar:getString()` and get the result. — Stéphane Péchard, Jan 14 '14 at 12:55
You will have to clarify. Show the Lua code you would like to be able to write. Have you looked at https://github.com/torus/Lua-Objective-C-Bridge? You might be able to find solution by looking at how Wax bridged Lua and Objective-C (Wax is no longer maintained but that's beside the point, the techniques should still apply). — Oliver, Jan 15 '14 at 04:44
@Schollii I added the Lua code I want to write, just a simple function using a non-nil `luaVar` variable. I already looked at what you proposed but `Lua-Objective-C-Bridge` is not iOS-oriented and `Wax` is just extremely difficult to port to a modern iOS project. In fact, I needed something simpler that a full solution such as those. I found the answer anyway, thanks again! — Stéphane Péchard, Jan 15 '14 at 08:55

score 0 · Accepted Answer · answered Jan 15 '14 at 08:57

0

Found it myself. It was just a missing line at the end of the newScriptObject function which sets the defined variable as a Lua global:

lua_setglobal(L, SCRIPT_OBJECT_LUA_KEY);

answered Jan 15 '14 at 08:57

Stéphane Péchard

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Bind an Objective-C object to an existent Lua variable

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