ETS 本地数据存储

ETS 是 Erlang 表存储系统，它提供基于哈希的数据存储和访问功能。这些功能在恒定时间内运行。ETS 数据在进程运行期间存储在该进程中。

以下是如何在 ETS 中使用一些简单函数的示例。请注意，由于“goofy”没有姓氏，所以表格不是正方形的。

示例程序：test_ets.erl

-module(test_ets).
-compile(export_all).

start() -> start( mouse ).

start( Animal ) ->
	Kingdom = ets:new( 'magic',  [] ),
	% note: table is not square
	populate( Kingdom, [{micky,mouse}, {mini,mouse}, {goofy}] ),
	Member = ets:member( Kingdom, micky ),
	io:format( " member ~w ~n ", [ Member ] ),
	%% show_next_key( Kingdom, micky ),
        %% Not work as expected in OTP 19.2
        %% Do a minor change
        FirstKey = ets:first(Kingdom),
        show_next_key(Kingdom, FirstKey),
	find_animal( Kingdom, Animal ).
	
show_next_key( _Kingdom, '$end_of_table' ) -> done;
show_next_key( Kingdom,  Key) ->
	Next = ets:next( Kingdom, Key ),
	io:format( " next ~w ~n ", [ Next ] ),
	show_next_key( Kingdom, Next ).

populate( _Kingdom, [] ) -> {done,start};
populate( Kingdom, [H | T] ) ->
		ets:insert( Kingdom, H ),
		populate( Kingdom, T ).
	
find_animal( Kingdom, Animal ) ->
	ets:match( Kingdom, { '$1', Animal } ).

% ==============
% sample output
% ==============
% 53> test_ets:start().
% member true 
%  next mini 
%  next goofy 
%  next '$end_of_table' 
%  [[mini],[micky]]