IfItQuacks: compile-time checked structural typing for C#

IfItQuacks lets you pass objects of unrelated types to a method, as long as they structurally satisfy an interface. The check happens at compile time and the call is redirected through a generated adapter - no reflection, no dynamic.

Download

IfItQuacks is available on NuGet.

dotnet add package IfItQuacks

Example usage

public interface IDoable
{
    void Do();
}

public class A
{
    public void Do() => Console.WriteLine("A.Do");
}

public static partial class Ops
{
    [DuckTyped]
    public static void Foo(IDoable doable) => doable.Do();
}

Ops.Foo(new A()); // A.Do

Under the hood the generator writes a small wrapper that implements the interface and replaces your call so it passes that wrapper instead:

// You write
Ops.Foo(new A());

// The generator emits (simplified)
struct A_As_IDoable(A value) : IDoable
{
    public void Do() => value.Do();
}

// and the compiler actually calls
Ops.Foo(new A_As_IDoable(new A()));

If A has no matching Do(), the build fails. See How does it work? for details.

Head over to Getting started for the setup.