We know that co-variance allows us to do things like this:
IEnumerable<object> objects;
IEnumerable<string> strings = new[] { "hello", "world" };
objects = strings;
This code compiles, and works, due to co-variance.
However, if I use a bound generic, I get an error, as in the example:
void Test<T>(T blah) where T : ISerializable
{
IEnumerable<T> x = new[] { blah };
IEnumerable<ISerializable> y;
y = x;
}
Gives the following error
[CS0266] Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<T>' to 'System.Collections.Generic.IEnumerable<System.Runtime.Serialization.ISerializable>'.
An explicit conversion exists (are you missing a cast?)
In my head, this should work. I suspected that this could be related to some incompatibility with value types, and this was true. If I change the signature to
void Test<T>(T blah) where T : class, ISerializable
the code compiles with no errors.
But why? And how is this related to the error message?
