See the following code snippet:
(IEnumerable<object>)new Dictionary<string, string>()
The above cast will throw an invalid cast exception.
Actually, IDictionary<TKey, TValue> also indirectly implements IEnumerable<out T>, because it also implements ICollection<T>. That is, the whole cast should be valid.
In fact, for me it is even more strange that if I run the whole cast on a debugger watch slot, it works!
What's going on?
That dictionary does implement IEnumerable<KeyValuePair<TKey, TValue>> and IEnumerable, but IEnumerable of a struct is not the same as IEnumerable of an object. Variance only works for reference-types. KeyValuePair<K, V> is a struct and not a class.
This does work at my end and should be the logical choice:
var x = (IEnumerable)new Dictionary<string, string>();
As a sample, this does work:
List<string> l = new List<string>();
var x = (IEnumerable<object>)l;
But this one doesn't:
List<DateTime> l2 = new List<DateTime>();
var x = (IEnumerable<object>)l2;
Clearly indicating the struct is the problem.
(Why it works in your Watch windows, I don't know)
I think this is because KeyValuePair is a Value-Type.
This would fail:
List<int> ints = new List<int>();
var objs = (IEnumerable<object>)ints;
This would work:
List<string> ints = new List<string>();
var objs = (IEnumerable<object>)ints;
same goes for the dictionary.
If you really can't live with plain IEnumerable, try this:
new Dictionary<string, string>().Cast<object>();
This is strange. Your code snippet works fine with .NET 4.0. I suggest you cast to IEnumerable.
Read: IDictionary Interface (MSDN)
