c＃ConcurrentDictionary包裝AddOrUpdate與懶惰不編譯

Question

我想創建一個新的類，將包裝當前.net ConcurrentDictionary，以確保GetOrAdd \ AddOrUpdate的添加委託將被確保只被調用一次。我在網絡上看到了一些解決方案，主要的一點是懶惰地包裝TValue，這樣可以添加許多懶惰物品，但只有一個可以生存並調用它的價值工廠。

這裏就是我想出：

public class LazyConcurrentDictionary<TKey, TValue> 
{ 
    private readonly ConcurrentDictionary<TKey, Lazy<TValue>> concurrentDictionary; 

    public LazyConcurrentDictionary() 
    { 
     this.concurrentDictionary = new ConcurrentDictionary<TKey, Lazy<TValue>>(); 
    } 

    public TValue GetOrAdd(TKey key, Func<TKey, TValue> valueFactory) 
    { 
     var lazyResult = this.concurrentDictionary.GetOrAdd(key, k => new Lazy<TValue>(() => valueFactory(k), LazyThreadSafetyMode.ExecutionAndPublication)); 

     return lazyResult.Value; 
    } 

    public TValue AddOrUpdate(TKey key, Func<TKey, TValue> addFactory, Func<TKey, TValue> updateFactory) 
    { 

     // this one fails with "Cannot convert lambda expression to type 'System.Lazy' because it is not a delegate type" 
     var lazyResult = this.concurrentDictionary.AddOrUpdate(key, (k) => new Lazy<TValue>(() => addFactory(k), LazyThreadSafetyMode.ExecutionAndPublication), updateFactory); 

     return lazyResult.Value; 
    } 
} 

我的問題是與AddOrUpdate簽名，我得到「無法轉換lambda表達式鍵入‘System.Lazy’，因爲它不是一個委託類型」

我在做什麼錯？

Answer 1

我想你錯過了這個函數的updateFactory的意思。它的功能從TKey,TValue到TValue，而不是從TKey到TValue，它應該從舊的計算一個更新的值。 所以，正確的語法，也許應該是這樣的：

public TValue AddOrUpdate(TKey key, Func<TKey, TValue> addFactory, 
            Func<TValue, TValue> updateFactory) 
{ 
    var lazyResult = this.concurrentDictionary.AddOrUpdate(key, 
    (k) => new Lazy<TValue>(() => addFactory(k), 
         LazyThreadSafetyMode.ExecutionAndPublication), 
    (k,v)=>new Lazy<TValue>(()=>updateFactory(v.Value))) 
    ); 

    return lazyResult.Value; 
} 

甚至（取決於你如何wnat使用它）：

public TValue AddOrUpdate(TKey key, Func<TKey, TValue> addFactory, 
            Func<TKey, TValue, TValue> updateFactory) 
{ 
    var lazyResult = this.concurrentDictionary.AddOrUpdate(key, 
    (k) => new Lazy<TValue>(() => addFactory(k), LazyThreadSafetyMode.ExecutionAndPublication), 
    (k,v)=>new Lazy<TValue>(()=>updateFactory(k, v.Value)) 
    ); 

    return lazyResult.Value; 
} 

當然