CacheTable.cs

abstract class CacheTable<TKey, TValue>
{
	public void Expire()
	{
		m_table = null;
	}

	abstract public IDictionary<TKey, TValue> CreateTable();

	public TValue Lookup(TKey key)
	{
		return table[key];
	}

	public TValue Lookup(TKey key, TValue defaultValue)
	{
		TValue value;
		if (!(table.TryGetValue(key, out value)))
			value = defaultValue;
		return value;
	}

	#region Internal

	private IDictionary<TKey, TValue> table
	{
		get
		{
			if (m_table == null)
				m_table = CreateTable();
			return m_table;
		}
	}
	private IDictionary<TKey, TValue> m_table = null;

	#endregion
}

class FooBarCacheTable : CacheTable<char, string>
{
	override public IDictionary<char, string> CreateTable()
	{
		return (
			new [] {
				"foo",
				"bar",
				"baz",
			}
			.ToLookup(x => x[0])
			.Select(xs => xs.OrderBy(x => x).First())
			.ToDictionary(x => x[0])
		);
	}
}