Question

I have a cache class which stores a list into a dictionary:

public class CacheList<T>
{
    private Dictionary<UInt64, T> _cacheItems = new Dictionary<UInt64, T>();

    public IList<T> GetItems()
    {
        return new List<T>(_cacheItems.Values);
    }

    public void Add(T item)
    {
        UInt64 key = (UInt64)(item.GetHashCode());

        if (!_cacheItems.ContainsKey(key))
            _cacheItems.Add(key, item);
    }
}

Now I am adding items to the dictionary by getting the Hashcode from the generic T. But I would like to specify which field / property I want to have as the key. Problem is it is a type T so it doesn’t know which properties are in this item.

How would I access a property from a generic item?

Answer 1

Maybe:

public class CacheList<T, TKey>
{
    private readonly Dictionary<TKey, T> _cacheItems = new Dictionary<TKey, T>();
    private readonly Func<T, TKey> selector;
    public CacheList(Func<T, TKey> selector)
    {
        this.selector = selector;
    }
    public IList<T> GetItems()
    {
        return new List<T>(_cacheItems.Values);
    }

    public bool Add(T item)
    {
        TKey key = selector(item);

        if (_cacheItems.ContainsKey(key)) { return false; }

        _cacheItems.Add(key, item);
        return true;
    }
    public bool TryGetValue(TKey key, out T value)
    {
        return _cacheItems.TryGetValue(key, out value);
    }
}

Then:

var dict = new CacheList<Customer,int>(c => c.CustomerId);