c# - 查找具有不同类型值的两个字典的并集

Question

问题

using System.Collections.Generic;
using System.Linq;

给定一个基类和 2 个派生类:

class Base{}
class Derived0 : Base{}
class Derived1 : Base{}

我有两本字典，类型为:

IDictionary<String, Derived0> d0 = ...;
IDictionary<String, Derived1> d1 = ...;

我想找到两个字典的并集，其类型应为 IDictionary<String, Base> 。 (我已经知道键在两个字典中都是唯一的，因此我不关心存在重复项时的行为。)

---

尝试

如果它们是同一类型I could use

var union = d0.Concat(d1);

但这给出了错误(使用 dmcs 编译):

Test.cs(15,20): error CS0411: The type arguments for method `System.Linq.Queryable.Concat<TSource>(this System.Linq.IQueryable<TSource>, System.Collections.Generic.IEnumerable<TSource>)' cannot be inferred from the usage. Try specifying the type arguments explicitly

如果我明确给出 Base作为类型参数:

IDictionary<string, Base> union = d0.Concat<Base>(d1);

它仍然不起作用:

Test.cs(15,42): error CS1928: Type `System.Collections.Generic.IDictionary<string,Derived0>' does not contain a member `Concat' and the best extension method overload `System.Linq.Enumerable.Concat<Base>(this System.Collections.Generic.IEnumerable<Base>, System.Collections.Generic.IEnumerable<Base>)' has some invalid arguments
/usr/lib/mono/gac/System.Core/4.0.0.0__b77a5c561934e089/System.Core.dll (Location of the symbol related to previous error)
Test.cs(15,42): error CS1929: Extension method instance type `System.Collections.Generic.IDictionary<string,Derived0>' cannot be converted to `System.Collections.Generic.IEnumerable<Base>'

原则上，方差在这里并不重要，因为我正在创建一个新的字典对象，但我不知道如何在类型系统中表示它。

Answer 1

IDictionary<TKey, TValue>和KeyValuePair<TKey, TValue>不是变体...所以:

var sequence0 = d0.Select(kvp => new KeyValuePair<String, Base>(kvp.Key, kvp.Value));
var sequence1 = d1.Select(kvp => new KeyValuePair<String, Base>(kvp.Key, kvp.Value));
var dictionaryOfBase = sequence0.Concat(sequence1).ToDictionary(kvp => kvp.Key, kvp => kvp.Value);