gb_trees:get/2

在树里查找一个键（如果存在的话）

用法：

get(Key, Tree) -> Val

内部实现：

%% This is a specialized version of 'lookup'.

-spec get(Key, Tree) -> Val when
      Key :: term(),
      Tree :: gb_tree(),
      Val :: term().

get(Key, {_, T}) ->
    get_1(Key, T).

get_1(Key, {Key1, _, Smaller, _}) when Key < Key1 ->
    get_1(Key, Smaller);
get_1(Key, {Key1, _, _, Bigger}) when Key > Key1 ->
    get_1(Key, Bigger);
get_1(_, {_, Value, _, _}) ->
    Value.

获取保存在树里的跟键 Key 相关的值。这里假设树里是存在这个键，否则将报错。

Tree1 = gb_trees:empty(),
Tree2 = gb_trees:enter(a, 1, Tree1),
gb_trees:get(a, Tree2).