Understanding the lack of static method in Interface in C#

In C# there is no way to define a static method in an interface:

interface IMyClass
{
    void MyMethod();  // this is fine
    static int MyStaticMethod();  // not allowed..
    static int MyOtherStaticMethod() { return 1; } // not allowed either
}

This lack of static method can be painful at times, and on the surface one feels there is no reason why it can’t/shouldn’t be supported by the language. But after ploughing through forum discussions and numerous questions on StackOverflow I start to understand why this is the case.

Practically, this is why having static method on the interface is confusing:

interface IMyClass
{
    static int MyStaticMethod();
}

class MyClassA : IMyClass
{
    static int MyStaticMethod() { return 1; }
}

class MyClassB : IMyClass
{
    static int MyStaticMethod() { return 2; }
}

So what does IMyClass.MyStaticMethod return?

Philosophically, an Interface defines a contract, when dealing with an interface you don’t have to know the implementation details but only what is available on the interface. Static method on the hand, are designed so that you have a well known location for a method/property and don’t need an instance of the object to work with it.

These two concepts are polar opposites, and you can’t mix the two together without breaking polymorphism!

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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.

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