ets:foldl/3

对 ETS 数据遍历循环操作

用法：

foldl(Function, Acc0, Tab) -> Acc1

内部实现：

-spec foldl(Function, Acc0, Tab) -> Acc1 when
      Function :: fun((Element :: term(), AccIn) -> AccOut),
      Tab :: tab(),
      Acc0 :: term(),
      Acc1 :: term(),
      AccIn :: term(),
      AccOut :: term().

foldl(F, Accu, T) ->
    ets:safe_fixtable(T, true),
    First = ets:first(T),
    try
        do_foldl(F, Accu, First, T)
    after
	ets:safe_fixtable(T, false)
    end.

do_foldl(F, Accu0, Key, T) ->
    case Key of
	'$end_of_table' ->
	    Accu0;
	_ ->
	    do_foldl(F,
		     lists:foldl(F, Accu0, ets:lookup(T, Key)),
		     ets:next(T, Key), T)
    end.

对 ETS 数据遍历循环操作，对数据遍历的规则跟 lists:foldl/3 一样。

Tab = ets:new(ets_tab, [named_table, set]),
ets:insert(Tab, [{a, 1}, {b, 2}, {c, 3}, {d, 4}, {e, 5}]),
ets:foldl(fun({_Key, Val}, AccVal) ->
    AccVal + Val
end, 0, Tab).