C＃方法中的静态参数

Question

I have doubt in C# about Static class usage in methods. Suppose that we have a method with two parameter int and Enum in another class.

public void DemoMethod(int pricePerTenant , TenantType tenantType){
    //Method implementation    
}

If we implement a static class instead of Enum, C# don't allow passing static class as method parameter

public static class TenantType
{
   public static readonly int TenantAdmin = 1;
   public static readonly int TenantUser = 2;
   public static readonly int PublicUser = 3;
}

//With static class parameters
public void DemoMethod(int pricePerTenant , TenantType tenantType){
    //Method implementation    
}

Why C# CLR refuse to take Static class as parameters?

Thanks

Answer 1

You can never instantiate a TenantType - so the only value you could possibly pass into DemoMethod would be null . Think about how you'd be calling the method - if you were expecting to call (say) DemoMethod(10, TenantType.TenantUser) then that would be an int argument instead of a TenantType anyway.

Basically, a static class never has instances, so it doesn't make sense to allow them to be used anywhere that you'd be considering instances - including method parameters and type arguments. You should be grateful that C# is catching your error so early, basically - that's one of the benefits of static classes.

In this case it sounds like really you should have an enum instead:

public enum TenantType
{
    Admin = 1,
    User = 2,
    PublicUser = 3
}

At that point you can accept it as a parameter - you'll still be able to call DemoMethod(10, TenantType.User) , but in a type-safe way where unless the method really cares about the integer mapping, it never has to see it.

Answer 2

Because if you specify TenantType tenantType as a parameter, you tell C#, that you require an instance of TenantType here. And since you don't pass one, it won't work.

This, in turn, will:

public void DemoMethod(int pricePerTenant, int tenantType) {

}

DemoMethod(3, TenantType.TenantAdmin);

But . There is a method similar to yours, which will actually work:

public class TenantType {

    private int value;

    private TenantType(int newValue)
    {
        value = newValue;
    }

    public override bool Equals(object obj)
    {
        return (obj is TenantType && (obj as TenantType).value == this.value;
    }

    public override int GetHashCode()
    {
        return value;
    }

    public static bool operator == (TenantType left, TenantType right)
    {
        return left.Equals(right);
    }

    public static bool operator != (TenantType left, TenantType right)
    {
        return !(left.Equals(right));
    }

    public static TenantType Admin = new TenantType(1);
    public static TenantType User = new TenantType(2);
    public static TenantType PublicUser = new TenantType(3);
}

public void DemoMethod(int pricePerTenant, TenantType tenantType)
{

}

DemoMethod(4, TenantType.Admin);

As you see, this requires a lot more work than the simplest solution with enums (after all, this is precisely what they were created for).