Generic base class constructor

Using this generic base class:

public abstract class Logic<U> where U : class
{
    protected U m_provider;
    public Logic(U provider)
    {
        m_provider = provider;
    }
}

I’m trying to create a base test class for unit test:

public class LogicBaseTest<T, U> where T : Logic <U>, new()  where U: class
{
    protected T m_logic;
    protected U m_provider;

    [OneTimeSetUp]
    public virtual void OneTimeSetup()
    {
        m_provider = (U)Substitute.For<IInterface>();

        m_logic = new T(m_provider);
    }
}

It complains on the constructor, it requests for the new() constrain but when I add it then it complains that the constructor cannot take parameters.

I could add a method to populate the provider but I’m wondering whether it could be done in the constructor.

>Solution :

So you have two problems here:

1. LogicBaseTest needs to know how to instantiate a Logic<U>.
2. Logic<U> requires a U in the constructor.

My proposed solution to it is to pass a factory delegate into the base test class and remove the new() requirement. Then your setup can construct the Logic class using the factory:

public class LogicBaseTest<T, U> 
    where T : Logic<U>
    where U: class
{

    protected readonly Func<U, T> _factory;

    public LogicBaseTest(Func<U, T> factory)
    {
        _factory = factory;
    }

    [OneTimeSetUp]
    public virtual void OneTimeSetup()
    {
        m_provider = (U)Substitute.For<IInterface>();
        m_logic = _factory(m_provider);
    }
}

In the derived test class you just have to tell the base class how to new up a Logic<U>:

public class DerivedTest : LogicBaseTest<Logic<MyUType>, MyUType>
{
    public DerivedTest()
        : this(u => new Logic<MyUType>(u))
    {
    }
}