Gets or sets the value associated with a given key. When getting a value, if this key is not found in the collection, then an ArgumentException is thrown. When setting a value, the value replaces any existing value in the dictionary.

public override sealed TValue this[
	TKey key
] { get; set; }

public:
virtual property TValue default[TKey key] {
	TValue get (TKey key) override sealed;
	void set (TKey key, TValue value) override sealed;
}