Reverse Patch

Previous chapters covered "adding things to game methods." Reverse Patch is the opposite: taking a game method "out" and turning it into a method you can call yourself.

Why Reverse Patch?

Sometimes game methods aren't publicly accessible, or their logic can't be triggered through parameters. Reverse Patch lets you call any game method — including private methods, static methods, and even constructors.

Declaring a Reverse Patch

[HarmonyPatch(typeof(SomeGameClass), nameof(SomeGameClass.SomePrivateMethod))]
public static class SomePrivateMethod_Reverse
{
    // Signature must be compatible with the target method; Harmony generates the implementation
    public static void SomePrivateMethod(SomeGameClass instance) { }
}

Key points:

• The class declares the target with [HarmonyPatch]
• The patch method name is arbitrary, but the signature must be compatible with the target method
• For instance methods, the first parameter is instance

Using It

// Before: SomePrivateMethod is private and can't be called
// After:
var game = new SomeGameClass();
SomePrivateMethod_Reverse.SomePrivateMethod(game);

Declaring with Attribute: ReversePatchType

A more common approach uses [HarmonyReversePatch]:

[HarmonyPatch(typeof(SomeGameClass), nameof(SomeGameClass.SomePrivateMethod))]
public static class SomePrivateMethod_Reverse
{
    [HarmonyReversePatch]
    public static void SomePrivateMethod(SomeGameClass instance)
    {
        // This method body won't actually execute; Harmony replaces it with a call to the target method
        throw new NotImplementedException();
    }
}

Writing throw new NotImplementedException() as the method body is a convention — at runtime, Harmony replaces it with generated IL that calls the target method.

Creating a Reverse Patch Manually

Without attributes, generate with code:

var target = AccessTools.Method(typeof(SomeGameClass), "SomePrivateMethod");
var stub = AccessTools.Method(typeof(MyPatches), nameof(MyPatches.SomePrivateMethod));

var instance = new Harmony(MyMod.Harmony.Id);
var reverse = instance.CreateReversePatcher(target, new HarmonyMethod(stub));
reverse.Patch();

What You Learned

• Reverse Patch can call any game method (including private ones)
• [HarmonyReversePatch] and the placeholder method body
• Creating a Reverse Patch manually

Next Step

Back to the main topic: adding settings to your Mod → Settings System