public static IBinaryTree <TResult> Select <TResult, T>(
this IBinaryTree <T> tree,
Func <T, TResult> selector)
{
if (tree == null)
{
throw new ArgumentNullException(nameof(tree));
}
if (selector == null)
{
throw new ArgumentNullException(nameof(selector));
}
var visitor = new SelectBinaryTreeVisitor <T, TResult>(selector);
return(tree.Accept(visitor));
}