Design patterns Factory Flyweight Factory (C#)


Example

In simple words:

A Flyweight factory that for a given, already known, key will always give the same object as response. For new keys will create the instance and return it.

Using the factory:

ISomeFactory<string, object> factory = new FlyweightFactory<string, object>();

var result1 = factory.GetSomeItem("string 1");
var result2 = factory.GetSomeItem("string 2");
var result3 = factory.GetSomeItem("string 1");

//Objects from different keys
bool shouldBeFalse = result1.Equals(result2);

//Objects from same key
bool shouldBeTrue = result1.Equals(result3);

Implementation:

public interface ISomeFactory<TKey,TResult> where TResult : new()
{
    TResult GetSomeItem(TKey key);
}

public class FlyweightFactory<TKey, TResult> : ISomeFactory<TKey, TResult> where TResult : new()
{
    public TResult GetSomeItem(TKey key)
    {
        TResult result;
        if(!Mapping.TryGetValue(key, out result))
        {
            result = new TResult();
            Mapping.Add(key, result);
        }
        return result;
    }

    public Dictionary<TKey, TResult> Mapping { get; set; } = new Dictionary<TKey, TResult>();
}

Extra Notes

I would recommend to add to this solution the use of an IoC Container (as explained in a different example here) instead of creating your own new instances. One can do it by adding a new registration for the TResult to the container and then resolving from it (instead of the dictionary in the example).