ObjectListExtensions.OfType should ignore null values

[wmrutten]

Concerning the extension method ObjectListExtensions.OfType in the Hl7.Fhir.Support library:

1. Why this custom method, as LINQ also provides a (generic) method OfType<T> with same behavior out of the box?
2. The LINQ OfType<T> method uses the is operator, which automatically skips/excludes null values but includes subclasses. The custom method compares runtime types, which throws an exception for null values and excludes subclasses.

Suggestions:

1. Remove this method, use LINQ instead
2. Or rewrite the method to behave exactly the same as the LINQ method (using is operator)
3. Or rename this method to e.g. OfExactType (only if the API depends on such behavior)

[ewoutkramer]

We cannot use the LINQ method here, since it's not the same. OfType in LINQ takes a compile-time specified generic parameter, this method takes a variable type parameter, which is passed at runtime and cannot be used with 'is'.

The behaviour of 'is' can be simulated with Type.IsAssignableFrom(), which is however much slower than direct type comparisons.

I do agree this method is way too specific to be a public extension on IEnumerable, so I will consider inlining this, since it's hardly used.

[wmrutten]

Agreed, inlining seems appropriate here.

[mmsmits]

Decided to remove ObjectListExtensions entirely + tests. Since this is not used anyway.