结合“检查添加或获取”从词典(Combined “Check Add or Fetch” from Dictionary)

结合“检查添加或获取”从词典(Combined “Check Add or Fetch” from Dictionary)

我厌倦了这本词典的成语：

Dictionary<Guid,Contact> Contacts; //... if (!Contacts.ContainsKey(id)) { contact = new Contact(); Contacts[id] = contact; } else { contact = Contacts[id]; }

如果有一种语法允许新值从默认构造函数中隐式创建（如果它不存在的话）（毕竟，该字典知道值的类型）会很好。 任何人都看到了这样做的助手（如扩展方法）？

I'm tired of this dictionary idiom:

Dictionary<Guid,Contact> Contacts; //... if (!Contacts.ContainsKey(id)) { contact = new Contact(); Contacts[id] = contact; } else { contact = Contacts[id]; }

It would be nice if there was a syntax that permitted the new value to be created implicitly from a default constructor if it does not exist (the dictionary knows the type of the value, after all). Anyone seen a helper (such as an extension method) that does this?

最满意答案

执行：

public static TValue GetOrAdd<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key, Func<TValue> valueCreator) { TValue value; if (!dictionary.TryGetValue(key, out value)) { value = valueCreator(); dictionary.Add(key, value); } return value; } public static TValue GetOrAdd<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key) where TValue : new() { return dictionary.GetOrAdd(key, () => new TValue()); }

用法：

var contacts = new Dictionary<Guid, Contact>(); Guid id = ... contacts.GetOrAdd(id).Name = "Abc"; // ok since Contact has public parameterless ctor contacts.GetOrAdd(id, () => new Contact { Name = "John Doe" }).Age = 40;

Implementation:

public static TValue GetOrAdd<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key, Func<TValue> valueCreator) { TValue value; if (!dictionary.TryGetValue(key, out value)) { value = valueCreator(); dictionary.Add(key, value); } return value; } public static TValue GetOrAdd<TKey, TValue>(this IDictionary<TKey, TValue> dictionary, TKey key) where TValue : new() { return dictionary.GetOrAdd(key, () => new TValue()); }

Usage:

var contacts = new Dictionary<Guid, Contact>(); Guid id = ... contacts.GetOrAdd(id).Name = "Abc"; // ok since Contact has public parameterless ctor contacts.GetOrAdd(id, () => new Contact { Name = "John Doe" }).Age = 40;