C# - Adding objects that implement interfaces to a dictionary

Question

I have a dictionary:

private Dictionary<Type, IExample> examples;

I have two classes that implement the interface:

public class Example1 : IExample
{
}

public class Example2 : IExample
{
}

I have created a way to get an instance from the dictionary if it exists but am trying to figure out a way to instantiate a new object if it doesn't exist.

public T GetExample<T>() where T : IExample
{
    // Return the signal if it exists
    if (examples.ContainsKey(typeof(T)))
    {
        IExample value;

        if (!examples.TryGetValue(typeof(T), out value))
        {
            // unable to get value
        }

        return (T)value;
    }

    // Stuck on this line here. How exactly do I instantiate a new example if it doesn't exist.
    examples.Add(typeof(T), new );

    return default(T);
}

Is such a thing possible?

Answer 1

You would need to add a generic type parameter constraint on your generic method for parameter-less constructor and then you can instantiate the type T parameter like new T():

public T GetExample<T>() where T : IExample,class,new()
{
       IExample value;

       if (examples.TryGetValue(typeof(T), out value))
       {
           return (T)value;
       }


   T obj =  new T(); // create instance of T and use further down in code it's reference
   examples.Add(typeof(T),obj );

   return obj ;
}

and return default(T); would return null not a new instance of T as for class (Reference Types) default value is null, i doubt you want to do return new T(); there, which will create a new object and will return the reference to it back to caller.