Determine if object derives from collection type

Question

I want to determine if a generic object type ("T") method type parameter is a collection type. I would typically be sending T through as a Generic.List but it could be any collection type as this is used in a helper function.

Would I be best to test if it implements IEnumerable<T>?

If so, what would the code look like?

Update 14:17 GMT+10 Possibly extending on a solution here (however only works for List<T>'s not IEnumerable<T>'s when it should if List derives ?)

T currentObj;    
// works if currentObj is List<T>
currentObj.GetType().GetGenericTypeDefinition() == typeof(List<>)
// does not work if currentObj is List<T>
currentObj.GetType().GetGenericTypeDefinition() == typeof(IEnumerable<>)

Answer 1

This will be the simplest check..

if(Obj is ICollection)
{
    //Derived from ICollection
}
else
{
    //Not Derived from ICollection
}

Answer 2

You can use Type.GetInterface() with the mangled name.

private bool IsTAnEnumerable<T>(T x)
{
    return null != typeof(T).GetInterface("IEnumerable`1");
}