Sorry for the clumsy title, but SO wouldn't let me leave it at "implicit conversion not working as expected".
Consider this trivial generic type:
public class Foo<T> {
public T Bar;
public Foo(T bar) => Bar = bar;
public static implicit operator Foo<T>(T bar) => new(bar);
}
Notice the implicit conversion that (at least in my mind) should allow me to create a Foo<T> directly from any T like so:
int[] xs = new[] { 1, 2, 3 };
IEnumerable<int> ys = xs.AsEnumerable();
Foo<IEnumerable<int>> foo = ys; // CS0266
However the above will produce a compiler error:
CS0266: Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<int>' to 'Foo<System.Collections.Generic.IEnumerable<int>>'. An explicit conversion exists (are you missing a cast?)
Funnily enough, the below code is working without problems:
int[] xs = new[] { 1, 2, 3 };
Foo<IEnumerable<int>> foo = xs; // no error
And using an explicit cast "fixes" the compiler error, but crashes at runtime:
int[] xs = new[] { 1, 2, 3 };
IEnumerable<int> ys = xs.AsEnumerable();
Foo<IEnumerable<int>> foo = (Foo<IEnumerable<int>>)ys; // InvalidCastException
InvalidCastException: Unable to cast object of type 'System.Int32[]' to type 'Foo`1[System.Collections.Generic.IEnumerable`1[System.Int32]]'.
What is going on here? I'm totally stumped and don't have the slightest clue.
.NET Fiddle: https://dotnetfiddle.net/wNHUtl
