Concord lets a .NET mod patch methods while the app runs. You write the patch in C#, and Concord leaves the target assembly on disk alone.

Start here API reference

CampfireWarmthPatch.cs C#

[Patch]
abstract class CampfireWarmthPatch : Campfire
{
    [Inject(At.Return, nameof(GetWarmth))]
    void AfterGetWarmth(ControlHandle<int> ch)
    {
        ch.ReturnValue += 5;
    }
}

What a patch does

The example patch adds 5 to Campfire.GetWarmth(). Concord does not rewrite the method in the target assembly.

In the target assembly

GetWarmth() returns twice the amount of fuel.

Campfire.cs C#

public int GetWarmth()
{
    return fuel * 2;
}

At runtime

Concord sends each call through a wrapper that adds 5.

GetWarmth at runtime C#

public int GetWarmth()
{
    int result = fuel * 2;
    result += 5;
    return result;
}

Reading order

If this is your first Concord patch, read Start Here, Getting started, and Your first patch in order. Use the rest as references.

Make a patch

Getting started Add Concord.Ref. Pick the optional build tools you want. Your first patch Write and apply patches to the example Campfire class. Common tasks Find an example for each supported patch position.

Look it up

How patches work See how Concord builds a wrapper and installs the detour. Packages See what each NuGet package contains and whether you need it. Troubleshooting Look up an error or inspect the IL Concord generated. Roadmap Check what Concord does not support yet.