public abstract T this[
	int[] idx,
	Nullable<long> hashVal = null
] { get; set; }

Public MustOverride Default Property Item ( 
	idx As Integer(),
	Optional hashVal As Nullable(Of Long) = Nothing
) As T
	Get
	Set

public:
virtual property T default[array<int>^ idx, Nullable<long long> hashVal = nullptr] {
	T get (array<int>^ idx, Nullable<long long> hashVal = nullptr) abstract;
	void set (array<int>^ idx, Nullable<long long> hashVal = nullptr, T value) abstract;
}

abstract Item : 'T with get, set