Extract similar static members from derived classes elegantly-CodePudding

public class A : BaseClass
{
    public static readonly int Min = 0;
    public static readonly int Max = 20;
    public int Val { get; }
    public A(int val)
    {
        if (val < Min || val > Max)
            throw new ApplicationException("invalid val");
        Val = val;
    }
    public static A Add(A o1, A o2)
    {
        return new A(o1.Val   o2.Val);
    }
}

public class B : BaseClass
{
    public static readonly int Min = 0;
    public static readonly int Max = 100;
    public int Val { get; }
    public B(int val)
    {
        if (val < Min || val > Max)
            throw new ApplicationException("invalid val");
        Val = val;
    }
    public static B Add(B o1, B o2)
    {
        return new B(o1.Val   o2.Val);
    }
}

A and B are almost the same, so how to extract the static members (Min, Max, Add) and the constructor into BaseClass elegantly?

I tried generic constraints, but it requires a parameterless constructor.

CodePudding user response：

For now C# doesn't support static abstract members but, good news, .NET may support it in future: Static abstract members in interfaces . And

For .NET 6, you must enable preview features in your project to be able to mark an interface member as static abstract.

CodePudding user response：

Static members are underivable, use abstract/virtual properties.

public abstract class BaseClass
{
    public abstract int Min { get; }
    public abstract int Max { get; }
}

public class A : BaseClass
{
    public override int Min { get { return 0; } }
    public override int Max { get { return 20; } }
}

CodePudding user response：

Did not test, but I guess I'd go for Generics:

public abstract class BaseClass<T> where T:BaseClass<T>
{
    public int Val {get;}
    
    private Func<int, T> _tFactory;

    public BaseClass(int val, int min, int max, Func<int, T> factory)
    {
         Val = Guard( val, min, max, nameof(val) );
         _tFactory = factory;
    }

    private int Guard( int val, int min, int max, string varName )
    {
        if (val < min || val > max)
        {
            throw new ApplicationException($"Value of {varName} must be inside {min} to {max} (inclusive).");
        }
        return val;
    }

    public static T Add(T o1, T o2)
    {
         return o1.Add(o2);
    }
    
    private T Add(T o2)
    {
         return _tFactory(this.Val   o2.Val);
    }
}


public class A : BaseClass<A>
{
    public static readonly int Min = 0;
    public static readonly int Max = 20;
    public A(int val) : base( val, Min, Max, i => new A(i) )
    {
    }
}

public class B : BaseClass<B>
{
    public static readonly int Min = 0;
    public static readonly int Max = 100;
    public B(int val): base( val, Min, Max, i => new B(i) )
    {
    }
}