/// <summary>
/// Updates values of all keys. For each key in the dictionary, if
/// <code>updateFunc(key, this[key])</code> returns <code>None</code>, the
/// key is removed; if it returns <code>Some(newValue)</code>, the
/// current value is replaced with <c>newValue</c>.
/// </summary>
/// <param name="updateFunc">The updating function.</param>
/// <returns>The resulting dictionary.</returns>
public TreeDictionary <TKey, TValue, TComparer> MapPartial(Func <TKey, TValue, Optional <TValue> > updateFunc)
{
if (Count == 0)
{
return(this);
}
var newValue = updateFunc(_key, _value);
return(newValue.HasValue
? Unbalanced(newValue.Value, _left.MapPartial(updateFunc), _right.MapPartial(updateFunc))
: GlueUnbalanced(_left.MapPartial(updateFunc), _right.MapPartial(updateFunc)));
}