C# Dictionary elementSelector 与隐式 IEnumerable 转换斗争

Question

简单场景：

var d = new Dictionary<int, List<int>>();

Dictionary<int, IEnumerable<int>> d2 = d.ToDictionary(
    kv => kv.Key,
    kv => kv.Value // <-- the problem
    );

.

ERROR  CS0029 : Cannot implicitly convert from List<string> to IEnumerable<string>

我的（可耻的）解决方法：

Dictionary<int, IEnumerable<int>> d2 = d.ToDictionary(
    kv => kv.Key,
    kv => kv.Value.Where(x => true) // <-- back to being IEnumerable
    );

我没有足够的勇气去尝试这个并面对不可预见的后果:

Dictionary<int, IEnumerable<int>> d2 = d.ToDictionary(
    kv => kv.Key,
    kv => (IEnumerable<int>)kv.Value // <-- explicit cast
    );

有什么建议吗？

Answer 1

Dictionary<int, IEnumerable<int>> d2 = d.ToDictionary(
    kv => kv.Key,
    kv => kv.Value.Where(x => true).AsEnumerable() // <--
    );