gb_trees:map/2

树里的每一个键值对都调用执行一次函数

用法：

map(Function, Tree1) -> Tree2

内部实现：

-spec map(Function, Tree1) -> Tree2 when
      Function :: fun((K :: term(), V1 :: term()) -> V2 :: term()),
      Tree1 :: gb_tree(),
      Tree2 :: gb_tree().

map(F, {Size, Tree}) when is_function(F, 2) ->
    {Size, map_1(F, Tree)}.

map_1(_, nil) -> nil;
map_1(F, {K, V, Smaller, Larger}) ->
    {K, F(K, V), map_1(F, Smaller), map_1(F, Larger)}.

树 Tree1 里的每一个键值对都调用执行一次 Function 函数，最后返回跟树 Tree1 有同键和新值的一个新树 Tree2。

Orddict = orddict:from_list([{pear, 7}, {orange, 5}, {apple, 2}]),
Tree = gb_trees:from_orddict(Orddict),
Fun = fun(K, V) -> lists:concat([K, "+", V]) end,
gb_trees:map(Fun, Tree).