C#•7mo ago

Can I add a field to compiled class?

I'm making a mod for a game and I need to give a class some extra information. I don't have access to how its constructed so I can't do type building. I can't replace dll's because this is a plugin. Is what I need to do possible with those restrictions?

19 Replies

Jimmacle•7mo ago

do you actually need to modify the class or do you just need to associate information with it?

LudoCryptOP•7mo ago

I need to give it a variable so i can use it inside the class. I have a thing for like hooking into a method to add code to it, and I need to do that, but I need to use a variable specific to the class

Jimmacle•7mo ago

https://learn.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.conditionalweaktable-2?view=net-8.0 is a way to associate data with an object

ConditionalWeakTable Class (System.Runtime.CompilerServices)

Enables compilers to dynamically attach object fields to managed objects.

Jimmacle•7mo ago

it's like a dictionary that automatically cleans up entries when the key is GCed

LudoCryptOP•7mo ago

I KNEW TGHERE WAS A BETTER WAY TO DO THAT thank you

Jimmacle•7mo ago

so instead of modifying the class directly you can use one of these and for each class add an entry with the class as the key and your custom data as the value i'd personally write some extension methods to make it more convenient to use like int GetMyInt(this ClassICantModify obj)

LudoCryptOP•7mo ago

Where would I put that

Jimmacle•7mo ago

sec, i'll wite a more thorough example

public class MyExtraData
{
    public string MyString { get; set; }
    public int MyInt { get; set; }
}

public static class ClassExtendedData
{
    private static readonly ConditionalWeakTable<object, MyExtraData> Table = new();

    public static MyExtraData GetMyExtraData(this object obj)
    {
        if (Table.TryGetValue(obj, out var data))
            return data;

        data = new MyExtraData();
        Table.Add(obj, data);
        return data;
    }
}

public class MyExtraData
{
    public string MyString { get; set; }
    public int MyInt { get; set; }
}

public static class ClassExtendedData
{
    private static readonly ConditionalWeakTable<object, MyExtraData> Table = new();

    public static MyExtraData GetMyExtraData(this object obj)
    {
        if (Table.TryGetValue(obj, out var data))
            return data;

        data = new MyExtraData();
        Table.Add(obj, data);
        return data;
    }
}

then you'd use this inside the class you're patching like

var myExtraData = this.GetMyExtraData()

var myExtraData = this.GetMyExtraData()

LudoCryptOP•7mo ago

ohhh okay tysm

jcotton42•7mo ago

is CWT thread safe? ah yep

jcotton42•7mo ago

actually @LudoCrypt @Jimmacle, probably should use GetOrCreate https://learn.microsoft.com/en-us/dotnet/api/system.runtime.compilerservices.conditionalweaktable-2.getorcreatevalue?view=net-8.0

ConditionalWeakTable.GetOrCreateValue(TKey) Method (System.Runtime....

Atomically searches for a specified key in the table and returns the corresponding value. If the key does not exist in the table, the method invokes the parameterless constructor of the class that represents the table's value to create a value that is bound to the specified key.

jcotton42•7mo ago

rather than a separate check then add

Jimmacle•7mo ago

ah, yeah i just did it from limited memory of using it years ago

LudoCryptOP•7mo ago

ohh that might explain why the screen kept going black

Jimmacle•7mo ago

dunno about that, but it's more correct either way it only really affects the first time it's accessed

LudoCryptOP•7mo ago

well it only happens when i call the get data method so iunno

Jimmacle•7mo ago

there's probably another issue "screen goes black" isn't much info to go on

LudoCryptOP•7mo ago

yea which is why i didnt say anything

TilionDC•7mo ago

if you are using Unity, chances are that you can use BepInEx lib

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Can I add a field to compiled class?