Microsoft.Extensions.DependencyInjection can not register type which implement static abstract memer interface

Question

I can not register the type Foo as 'IFoo' when IFoo has static abstract member. Is it a bug? Or, how can I register this type as interface?

repo

Program.cs

using Microsoft.Extensions.DependencyInjection;

// these line works!
IFoo foo = new Foo();
Foo.GetCount();

var services = new ServiceCollection();
services.AddSingleton(); // why this line can not compile?

// error message:
// The interface 'IFoo' type cannot be used as a type argument for type parameter 'TService'.
// The interface has static abstract members without implementations: int IFoo.GetCount()

public interface IFoo
{
    static abstract int GetCount();
}

public class Foo : IFoo
{
    public static int GetCount()
    {
        return 1;
    }
}

StaticAbstractMemberInInterfaceIssue.csproj



  
    Exe
    net8.0
    enable
    enable

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Accepted Answer

Hi @William Liu ,Welcome to Microsoft Q&A,

In C#, static abstract members in an interface are intended to be used in scenarios involving generic math or other compile-time polymorphism, but they can't be instantiated directly or used in the context of dependency injection.

You can use it like this:

using Microsoft.Extensions.DependencyInjection;

public interface IFoo
{
    // Removed static abstract member
}

public static class FooUtilities
{
    public static int GetCount()
    {
        return 1;
    }
}

public class Foo : IFoo
{
    // Instance members of Foo
}

class Program
{
    static void Main()
    {
        var services = new ServiceCollection();
        services.AddSingleton();

        var serviceProvider = services.BuildServiceProvider();
        IFoo foo = serviceProvider.GetRequiredService();

        int count = FooUtilities.GetCount();
        Console.WriteLine($"Count: {count}");
    }
}

Best Regards,

Jiale

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