C# implementation of LRU-cache

Question

I implemented a LRU-cache in C# and wanted to hear suggestions in making it more readable and maybe even more compact.

public class LRUCache<K, V>
{
 public int Capacity { get; }
 Dictionary<K, V> cache;
 K[] keyRingBuffer;
 int ringBufferIndex;
 int LRUIndex => (ringBufferIndex + 1) % Capacity;
 K LRU => keyRingBuffer[LRUIndex];
 public LRUCache(int capacity)
 {
 Capacity = capacity;
 cache = new Dictionary<K, V>(Capacity);
 keyRingBuffer = new K[Capacity];
 ringBufferIndex = 0;
 }
 public bool Contains(K key) => cache.ContainsKey(key);
 public int Size => cache.Count;
 public V Get(K key)
 {
 if (cache.TryGetValue(key, out var value))
 {
 keyRingBuffer[LRUIndex] = key;
 ringBufferIndex = LRUIndex;
 return value;
 }
 throw new Exception($"Element for key {key} not in cache");
 }
 public void Add(K key, V val)
 {
 if (cache.Count >= Capacity) cache.Remove(LRU);
 ringBufferIndex = LRUIndex;
 keyRingBuffer[ringBufferIndex] = key;
 cache.Add(key, val);
 }
}

I would love it to be more like -- how Robert Martin says -- "well written prose".

• Stack crashed: Looks like you are evicting the "most" recently used element, not least recently used.

Answer 1

First make it right. Then worry about readability, compactness, etc.

Consider the following use case:

var foos = new LRUCache<Foo, Bar>(2);
foos.Add(foo1, bar1);
foos.Add(foo2, bar2);
Quux(foos.Get(foo1));
Quux(foos.Get(foo1));
// The least recently used key is foo2, so it should be evicted
foos.Add(foo3, bar3);
Assert(foos.Contains(foo1));

Why does it fail?