/// <summary>
/// Updates values of all keys. For each key in the dictionary, the
/// value is replaced with <code>func(key, this[key])</code>.
/// </summary>
/// <typeparam name="TValue1">The type of the values in the returned dictionary.</typeparam>
/// <param name="func">The updating function.</param>
/// <returns>The resulting dictionary.</returns>
public TreeDictionary <TKey, TValue1, TComparer> MapPartial <TValue1>(Func <TKey, TValue, Optional <TValue1> > func)
{
if (Count == 0)
{
return(TreeDictionary <TKey, TValue1, TComparer> .Empty);
}
var newValue = func(_key, _value);
return(newValue.HasValue
? TreeDictionary <TKey, TValue1, TComparer> .Unbalanced(_key, newValue.Value, _left.MapPartial(func), _right.MapPartial(func))
: TreeDictionary <TKey, TValue1, TComparer> .GlueUnbalanced(_left.MapPartial(func), _right.MapPartial(func)));
}
