MentalDesk.DuckType

This is a duck typing library for C#. It allows you treat any object as if it implements any interface, so long as it has all the members required to do so.

Whilst dynamic types in C# allow you to do this, they do so at the expense of static typing and so expose you to the possibility of runtime errors.

By contrast, MentalDesk.DuckType uses source generators to create adapters around the objects that you want to duck type, so any changes to the members of those classes that would break the interface contract will result in a compiler error from the generated source code.

Installation

To get started, add MentalDesk.DuckType to your project by running the following command:

dotnet add package MentalDesk.DuckType

Usage

Imagine you have the following types:

class Duck
{
    public void Quack() => Console.WriteLine("Quack!");
}

class Derek
{
    public void Quack() => Console.WriteLine("quack...");
}

public interface IDuck
{
    public void Quack();
}

Derek and Duck can both clearly quack, and you want to be able to do something like this:

var duck = new Duck();
var derek = new Derek();
foreach (var d in [duck, derek]) // <-- this wont compile
{
    d.Quack();
}

Using MentalDesk.DuckType you can add a couple of assembly attributes to your project:

[assembly: DuckType<Duck, IDuck>]
[assembly: DuckType<Derek, IDuck>]

These DuckType<TClass, TInterface> attributes will trigger the duck typing source generators.

And then you can do this:

var duck = new Duck();
var derek = new Derek();
IDuck[] ducks = [ duck.AsIDuck(), derek.AsIDuck() ];
foreach (var d in ducks)
{
    d.Quack();
}

Behind the scenes, MentalDesk.DuckType has generated adapter classes wrapping Duck and Derek and also created some AsIDuck() extension methods that allow you to easily convert these to IDuck instances and leverage any common properties or methods that you've defined in the IDuck interface. It's statically typed, so it's safe and you don't have to write loads of code to make it work.