How can I parse a LuaTable in C#?

Question

I am at a complete loss with the syntax to parse a LuaTable. I have a table that follows the following structure:

mission = 
{
    ["coalition"] = 
    {
        ["blue"] = 
        {
            ["bullseye"] = 
            {
                ["y"] = -378451.53125,
                ["x"] = -178644.117188,
            }, -- end of ["bullseye"]
            ["country"] = 
            {
                [1] = 
                {
                    ["plane"] = 
                    {
                        ["group"] = 
                        {
                            [1] = 
                            {
                                ["hiddenOnPlanner"] = false,
                                ["tasks"] = {},
                                ["radioSet"] = false,
                                ["task"] = "AFAC",
                                ["uncontrolled"] = false,
                                ["hiddenOnMFD"] = false,
                                ["taskSelected"] = true,
                                ["route"] = 
                                {..............

and I am doing the following in my Winforms C# application (just a button triggering this code to test):

private void button29_Click_1(object sender, EventArgs e)
{
    Lua lua = new Lua();
    string s = File.ReadAllText("C:\\Users\\username\\Desktop\\mission");
    lua.DoString(s);
    var res = lua["mission.coalition.blue.country"];
    var bluePlanes = lua["mission.coalition.blue.country.1"];

    LuaTable tb = (LuaTable)res;
    Dictionary<object, object> dict = lua.GetTableDict(tb);
    Console.WriteLine("First chunk of code:");
    foreach (KeyValuePair<object, object> de in dict)
    {
        Console.WriteLine("{0} {1}", de.Key.ToString(), de.Value.ToString());
    }

    tb = (LuaTable)bluePlanes ;
    dict = lua.GetTableDict(tb);
    Console.WriteLine("Second chunk of code:");
    foreach (KeyValuePair<object, object> de in dict)
    {
        Console.WriteLine("{0} {1}", de.Key.ToString(), de.Value.ToString());
    }
}

The first chunk works but as soon as I stumble upon one of the elements in square brackets without quotes (e.g. [1]) null is returned. I have checked that manually adding the quotes solves this, but In the Watch view, I can see there are keys and values, just that I cannot index those. Any suggestion?

This is the console output:

First chunk of code:
1 table
Exception thrown: 'System.ArgumentNullException' in NLua.dll
Value cannot be null.

However, the information is shown in the Watch window: [![Watch window screenshot][1]][1]

Additionally, I thought of converting the table to JSON and using a C# class, but I cannot manage to do that from C# (tried using NLua to run a script in Lua that converts the table to JSON, but unsuccessfully, as I did not manage to reference the required Lua libraries)

Edit: adding a minimal structure to show the issue as requested in comments

    ["coalition"] = 
    {
        ["blue"] = 
        {
            ["country"] = 
            {
                [1] = 
                {
                }
            }
        }
    }

With this minimal structure, I am able to address up to coalition.blue.country, but would not be able to access the contenta under [1] which is the only element without double quotes [1]: https://i.sstatic.net/263XtjsM.png

Is there any chance you could cut the example and code down to the minimum required to illustrate the problem? That way someone will be happier to try and reproduce the issue. And there's also a chance that by doing that you find the answer yourself. — iakobski
– iakobski, Commented Oct 12, 2024 at 15:27
@iakobski: I have just added a minimal structure at the bottom. It does not make a big difference. My problem is still not being able to access elements without quotes — Francisco Benito
– Francisco Benito, Commented Oct 12, 2024 at 21:59
Thank you. I can not test in one week, just leaving on a trip, but you already clarified some doubts. Thanks for the well explained answer!! — Francisco Benito
– Francisco Benito, Commented Oct 13, 2024 at 20:22

iakobski · Accepted Answer · 2024-10-13 16:05:02Z

Unlike Lua, C# is a strongly typed language. So 1 is a number, and "1" is a string containing the character 1 and they can't be used interchangeably. Your line lua["mission.coalition.blue.country.1"]; is looking for the element with key "1" - a string key - on "country" and it can't find it, so you get a null returned.

You will need to split into two steps, one for the string key, the other for the number key. The NLua library transforms integers into the C# long type.

public void LuaTest()
{
    const string luaData = @"coalition = 
    {
        [""blue""] = 
        {
            [""country""] = 
            {
                [1] = 
                {
                    [""hiddenOnPlanner""] = false,
                    [""tasks""] = {},
                    [""radioSet""] = false
                }
            }
        }
    }";
    Lua lua = new Lua();
    lua.DoString(luaData);

    var country = lua["coalition.blue.country"] as LuaTable;
    if (country is null)
        throw new InvalidOperationException("Didn't find coalition.blue.country");
    var bluePlanes = country[1L] as LuaTable;
    if (bluePlanes is null)
        throw new InvalidOperationException("Didn't find item 1 on country");
    var dict = lua.GetTableDict(bluePlanes);

    Console.WriteLine("Second chunk of code:");
    foreach (KeyValuePair<object, object> de in dict)
    {
        Console.WriteLine($"{de.Key} {de.Value}");
    }
}

You'll notice that I've also added some checks for null. This is good practice: instead of a NullReferenceException at some point later in the code, you know exactly when something returned null that you were not expecting.

Output:

Second chunk of code:
radioSet False
hiddenOnPlanner False
tasks table

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