Static Virtual Methods in C# 12: Complete Guide

Are static methods finally getting their moment in the polymorphism spotlight? With C# 12, they just might.

Microsoft has introduced static virtual methods in interfaces—a long-requested feature that brings static polymorphism into mainstream .NET development. If you’ve ever felt constrained by the traditional object-oriented rules, this feature is a game-changer. Let’s break it down.

What Are Static Virtual Methods?

At its core, a static virtual method allows an interface to declare a static method that must be implemented by any type that implements the interface. Sounds contradictory? Virtual methods are dynamic; static methods are, well, static. So how can they be both?

C# 12 resolves this paradox by enabling compile-time polymorphism via static members. Unlike instance methods, which rely on runtime dispatch, static virtual methods are resolved at compile time using generics.

Historical Context

Before C# 12:

• Interfaces couldn’t define static members.
• Generic algorithms needed awkward workarounds like static helper classes.

With C# 12:

• Interfaces can declare static abstract or virtual methods.
• Generic algorithms can call static members on generic types that implement an interface.

Use Case Scenarios

• Mathematical operations (like generic Add, Multiply for numeric types).
• Operator overloading for generic types.
• Static factory methods for generic instances.

Syntax and Key Concepts

Here’s how you define a static virtual method:

public interface IMyOperator<T>
    where T : IMyOperator<T>
{
    static abstract T operator +(T left, T right);
}

In this case, any type implementing IMyOperator<T> must provide an implementation for the + operator.

Comparison

Key Terminology

• static abstract: Enforces implementation in the implementing type.
• static virtual: Allows a default implementation in the interface, which can be overridden.

Practical Examples

Example 1: Operator Overloading

public interface IAddable<T>
    where T : IAddable<T>
{
    static abstract T operator +(T left, T right);
}

public struct MyNumber : IAddable<MyNumber>
{
    public int Value;

    public MyNumber(int value) => Value = value;

    public static MyNumber operator +(MyNumber a, MyNumber b)
        => new MyNumber(a.Value + b.Value);
}

You can now write generic methods that rely on +:

public static T Add<T>(T a, T b) where T : IAddable<T>
{
    return a + b;
}

This eliminates the need for helper classes or delegates. It’s pure, readable, and strongly typed.

Example 2: Generic Math Interface

public interface INumber<T>
    where T : INumber<T>
{
    static abstract T One { get; }
    static abstract T Zero { get; }
    static abstract T operator +(T a, T b);
}

public struct MyInt : INumber<MyInt>
{
    public int Value;

    public MyInt(int value) => Value = value;

    public static MyInt One => new MyInt(1);
    public static MyInt Zero => new MyInt(0);
    public static MyInt operator +(MyInt a, MyInt b)
        => new MyInt(a.Value + b.Value);
}

Now, your math code becomes reusable across types:

public static T Sum<T>(T[] values) where T : INumber<T>
{
    T sum = T.Zero;
    foreach (var v in values)
        sum += v;
    return sum;
}

Best Practices and Pitfalls

Dos

• Use static abstract for mandatory implementation.
• Use static virtual to provide default behavior.
• Combine with generic constraints for powerfully reusable code.

Don’ts

• Don’t expect runtime polymorphism.
• Don’t overuse; keep readability in mind.

Tips

• Debugging? Check if your generic constraints are met.
• Testing? Use unit tests on generic methods with mock types.

When to Use (and Not Use) Static Virtual Methods

Use Them When:

• You need generic math or operator logic.
• You want to enforce static API contracts.
• You need reusable static logic across multiple types.

Avoid When:

• You need dynamic dispatch.
• Your team is not familiar with advanced generics.

FAQ: Static Virtual Methods in C# 12 Explained

Conclusion: Static Goes Polymorphic

Static virtual methods in C# 12 break the long-standing boundary between static logic and polymorphism. Whether you’re building mathematical libraries or simplifying generic algorithms, they offer a new way to write concise, powerful, and reusable code.

Now it’s your turn: implement a static virtual interface in your project and see how much boilerplate you can eliminate. Push the limits of your generic codebase, share your findings with your team, and explore how this shift can lead to cleaner architecture and smarter abstractions.