Confusing result of "GetElementType" on arrays and generic lists

Question

Generic list:

var elementType1 = typeof (List<A>).GetElementType();

Array:

var elementType = typeof (A[]).GetElementType();

Why do I only get the element type of an array? How could I get the element type of a generic list? (remark: the generic list is boxed)

Uropod

Could you clarify what your remark "the generic list is boxed" means? – Chromite

boxed means that you only have this list as an object. – Uropod

That's not boxing. Boxing only applies to value-types. – Chromite

@Chromite what is this then called? – Uropod

List<T> is a reference-type; a value (in general : expression) of such a type is a reference to an object. I'm guessing you just have a variable of a less-specific type (e.g. object) that refers to a List<SomeT> instance. That's just about assignment-compatibility, not boxing. It's a representation-preserving conversion; no boxing happens. – Chromite

Answer 1

GetElementType only gets the element-type for array, pointer and reference types.

When overridden in a derived class, returns the Type of the object encompassed or referred to by the current array, pointer or reference type

The reflection API doesn't "know" that List<T> is a generic container and that the type-argument of one of its constructed types is representative of the type of the elements it contains.

Use the GetGenericArguments method instead to get the type-arguments of the constructed type:

var elementType1 = typeof(List<A>).GetGenericArguments().Single();

Chromite

is there also a good approach to find out if I have a generic list or an array? I could proof for null and then use your solution, but maybe there is something better. – Uropod

Array = type.IsArray. ListT = type.GetGenericTypeDefinition() == typeof(List<>) (You will also need to verify that the type is a constructed generic type). – Chromite

Answer 2

var elementType1 = typeof(List<A>).GetGenericArguments()[0]; 
var elementType = typeof(int[]).GetElementType();

Consecutive