.Net Tips – How to determine if a type implements a generic interface type

When you have a generic interface such as:

public interface IInitializable<T>
{
    bool IsInitialized { get; }
    void Initialize(T initObject);
}

It’s easy to check whether a given instance implements the IInitializable interface with a specific T:

public class IntInitializable : IInitializable<int>
{
    public bool IsInitialized { get; private set; }
    public void Initialize(int initObject) { IsInitialized = true; }
}
…
var intInit = new IntInitializable();
Console.WriteLine(intInit is IInitializable<int>);  // outputs TRUE

But what if you want to find out if a type implements the IInitializable interface of an arbitrary T? You won’t be able to simply get away with this:

Console.WriteLine(intInit is IInitializable<>);  // doesn't compile

Instead, you can do something like this:

var isIInitializable = 
    intInit.GetType()
           .GetInterfaces()
           .Any(i => i.IsGenericType && 
                     i.GetGenericTypeDefinition() == typeof(IInitializable<>));

And if you want to find out what T is at runtime:

var t = intInit.GetType()
               .GetInterfaces()
               .First(i => i.IsGenericType && 
                           i.GetGenericTypeDefinition() == typeof(IInitializable<>))
               .GetGenericArguments()
               .First();

Enjoy what you’re reading? Subscribe to my newsletter and get more content on AWS and serverless technologies delivered straight to your inbox.


Yan Cui

I’m an AWS Serverless Hero and the author of Production-Ready Serverless. I have run production workload at scale in AWS for nearly 10 years and I have been an architect or principal engineer with a variety of industries ranging from banking, e-commerce, sports streaming to mobile gaming. I currently work as an independent consultant focused on AWS and serverless.

You can contact me via Email, Twitter and LinkedIn.

Hire me.


Check out my new course, Complete Guide to AWS Step Functions.

In this course, we’ll cover everything you need to know to use AWS Step Functions service effectively. Including basic concepts, HTTP and event triggers, activities, design patterns and best practices.

Get Your Copy