Generic class to create concrete class automatically

Question

Is there a way to take an interface, say:

/// <summary>
/// Interface containing operators which operate on T
/// </summary>
public interface IScalarOperators<T>
{
    // Adds two T objects
    IOperateScalar<T> OperatorAdd { get; }
    // Subtracts two T objects
    IOperateScalar<T> OperatorSubtract { get; }
    // Multiplies two T objects
    IOperateScalar<T> OperatorMultiply { get; }
}

// Class containing all the Scalar operators for a given T
class ScalarOperators<T> : IScalarOperators<T>
{
    public IOperateScalar<T> OperatorAdd { get; private set; }
    public IOperateScalar<T> OperatorSubtract { get; private set; }
    public IOperateScalar<T> OperatorMultiply { get; private set; }
    private ScalarOperators(IOperateScalar<T> add, IOperateScalar<T> subtract, IOperateScalar<T> multiply)
    {
        this.OperatorAdd = add;
        this.OperatorSubtract = subtract;
        this.OperatorMultiply = multiply;
    }

    public static ScalarOperators<bool> CreateBool()
    {
        return new ScalarOperators<bool>(new AddBool(), new SubtractBool(), new MultiplyBool());
    }

    public static ScalarOperators<int> CreateInt()
    {
        return new ScalarOperators<int>(new AddInt(), new SubtractInt(), new MultiplyInt());
    }

    // METHOD I WANT TO ADD
    public static ScalarOperators<T> Create()
    {
      // if T == bool
      // return CreateBool()
      // if T == int
      // return CreateInt()
      // else (no definition available for T)
      // return null
    }

    // I tried something like below, but it didn't work...
    public static ScalarOperators<T> Create<T>() where T: bool
    { return CreateBool(); }

    public static ScalarOperators<T> Create<T>() where T : int
    { return CreateInt(); }

    public static ScalarOperators<T> Create<T>()
    { return null; }
}

Notice, I'd like a generic Create method which creates the correct set of operators, but I'm not sure how to do it.

I'd like to use it to remove the parameter from this method:

    public static IMatrix<T> Add<T>(this IMatrix<T> matrix, IMatrix<T> other, IScalarOperators<T> operators)
    {
        JoinCells<T> joiner = new JoinCells<T>();
        return joiner.Join(matrix, other, null, operators.OperatorAdd);
    }

becomes

    public static IMatrix<T> Add<T>(this IMatrix<T> matrix, IMatrix<T> other)
    {
        JoinCells<T> joiner = new JoinCells<T>();
        return joiner.Join(matrix, other, null, ScalarOperators<T>.Create().OperatorAdd);
    }

Thanks for any help! Mainly, I just don't want to have to pass the scalarOperator object to the extension method, I'd prefer to have a 'default' since it is unlikely that the ScalarOperators will change for any T that is defined.

Answer 1

There are a few things happening here that I think should be addressed. You're trying to segregate your custom operators from the types that they operate on, which is confusing, and you're trying to take the very broad concept of generics and then specialize them.

For the first one, you're always going to use the same operators for the same type (at least, you're never going to try and use bool operators on an int type). There's no reason to complicate things by having a separate class for them. For the latter, generic classes and generic methods are meant to work the same for any given T. Granted, you very well could get the typeof(T) in your static factory method and compare against that for several specific cases, and then you'll have to change that for every new T that you want to handle because of this overly complicated generic operand structure.

I would recommend creating a generic interface for your operands and then implementing a wrapper for those types instead. For example, int can be wrapped like this.

public interface IScalarOperators<T>
{
    IScalarOperators<T> Add (IScalarOperators<T> rightSide);
    IScalarOperators<T> Subtract (IScalarOperators<T> rightSide);
    IScalarOperators<T> Multiply (IScalarOperators<T> rightSide);
    T Unwrap();
}

public interface IMatrix<T> where T : IScalarOperators<T> { /* whatever */ }

public class CustomInt : IScalarOperators<CustomInt>
{
    private readonly int number;
    public CustomInt(int number) { this.number = number; }
    public CustomInt Unwrap() { return this; }
    public IScalarOperators<CustomInt> Add(IScalarOperators<CustomInt> rightSide) { return new CustomInt(number + rightSide.Unwrap().number); }
    public IScalarOperators<CustomInt> Subtract(IScalarOperators<CustomInt> rightSide) { return new CustomInt(number - rightSide.Unwrap().number); }
    public IScalarOperators<CustomInt> Multiply(IScalarOperators<CustomInt> rightSide) { return new CustomInt(number * rightSide.Unwrap().number); }
}

At that point, you can operate on an IMatrix<CustomInt> through the IScalarOperators<T> interface and perform any exposed operations you want. As a rough example, assuming you have an exposed accessor called array, you could say IScalarOperators<T> result = matrix.array[0, 0].Add(matrix.array[0, 1]); and get a representation back of adding the two together. You could then perform any further operations on that, and so on.

Answer 2

i suggest making a factory of IScalarOperators instead of static class ( if your really need it to be static you could access it by static field ). you could register them at app startup and get them by this example metod:

 public IScalarOperators<T> Create<T>()
 {
    // check if exists in dictionary
    return (ScalarOperators<T>)dict[typeof(T)];
 }

dict will be of type Dictionary. The adventage is that you could add new IScalarOperators during application grow only by creating new implementing class and registering it in factory, casting is a drawback. Also you will have better seperation of concerns and ( in my opinion ) cleaner code.

Answer 3

What you need to do is get the type of T.

Your Create method could be like this:

public static ScalarOperators<T> Create()
{
    Type type = typeof(T); 
    if(type == typeof(bool))
      return CreateBool()
    if(type == typeof(int))
      return CreateInt()
    else
      return null
}