Question

当我尝试将SortedDictionary分配给IReadOnlyDictionary类型的变量时，编译器会拒绝它。我使用面向.NET 4.5的C＃项目使用Visual Studio 2013。

根据the documentation，SortedDictionary实现了IReadOnlyDictionary。反编译的库代码告诉我相同的。事实上，下面的代码剪断了打印＆＃34; True＆＃34;三次：

System.Diagnostics.Debug.WriteLine("Does it implement? " + typeof(SortedDictionary<int, int>).GetInterfaces().Contains(typeof(IReadOnlyDictionary<int, int>)));
System.Diagnostics.Debug.WriteLine("Is it assignable? " + typeof(IReadOnlyDictionary<int, int>).IsAssignableFrom(typeof(SortedDictionary<int, int>)));
var sorted = new SortedDictionary<int, int>();
var readOnly = (IReadOnlyDictionary<int, int>)sorted;
var roundTrip = (SortedDictionary<int, int>)readOnly;
// use ReferenceEquals to check if there's any explicit converter complicating things
System.Diagnostics.Debug.WriteLine("Do they cast? " + (object.ReferenceEquals(sorted, readOnly) && object.ReferenceEquals(readOnly, roundTrip)));

那为什么不编译？

IReadOnlyDictionary<int, int> readOnly = new SortedDictionary<int, int>();

Answer 1

因为它是在4.5之后的版本中引入的。我不知道哪一个，但MSDN显示4.6为＆＃34;当前版本＆＃34;并且没有办法如此4.5

为什么不能将IReadOnlyDictionary <tkey，tvalue =“”>从SortedDictionary <tkey，tvalue =“”>分配？

1 个答案: