* apply(M,F,A)要比直接调用调用对应的方法M:F(A1,A2...)要慢6~10倍，尽量避免使用 * BIFs是built-in functions的缩写代表这些方法是Erlang运行时系统的一部分 ```erlang %% binary_to_list VS bitstring_to_list 1> A = <<1:2, 23:6>>. <<"W">> 2> B = <<1:2, 23:5>>. <<55:7>> 3> binary_to_list(A). "W" 4> binary_to_list(B). ** exception error: bad argument in function binary_to_list/1 called as binary_to_list(<<55:7>>) 5> bitstring_to_list(A). "W" 6> bitstring_to_list(B). [<<55:7>>] ```  ```erlang statistics(wall_clock). {11405766,266} 返回指定类型的系统参数，当Type为wall_clock时，返回Erlang虚拟机运行至今所度过的时间和上次执行statistics(wall_clock)到这次执行之间的时间(精确到毫秒级)。 performs CPU time measurements context_switches||exact_reductions||garbage_collection||io||reductions||run_queue||runtime||scheduler_wall_time||wall_clock make_tuple( 2,“1” ) {“1”, “1”} localtime(). now(). localtime_to_universaltime({{1996,11,6},{14,45,17}}). {{年月日}，{时分秒}} 获取8小时时差的时间 list_to_existing_atom() tuple_size/1 byte_size/1 bit_size/1 round(10.5) -> 11, trunc( 10.5 ) -> 10 abs( -10 ) -> 10 12.8 rem 3 = 2. 8 div 3 = 2. get_stacktrace(). 查看最近的栈跟踪信息，栈跟踪信息包含当前调用函数的返回信息 system_info( process_limit ). 系统允许创建的进程上限 scheduler_id -> cpu 核心 schedulers process_count process_limit processes_used info memory(processes||total) node(). nodes(). nodes(hide). apply(Module, Fun, Arg). user_default.erl user_default.erl hello() -> "hello word!". 放入加载路径后，user_default模块中的任何函数可以直接调用而不需要给出模块名 put( key, value ) -> value||undefined get( key ) -> value||undefined float_to_list(7.12, [{decimals, 4}]). binary_to_integer(<<"10204">>). 10204 integer_to_binary(10204). <<"10204">> "7.1200" > float_to_list(7.12, [{decimals, 4}, compact]). "7.12" > float_to_binary(7.12, [{decimals, 4}]). <<"7.1200">> > float_to_binary(7.12, [{decimals, 4}, compact]). <<"7.12">> raise(Class, Reason, Stacktrace) -> no_return() Types:      Class = error | exit | throw      Reason = term()      Stacktrace = raise_stacktrace()      raise_stacktrace() = [{module(), atom(), arity() | [term()]} |{function(), [term()]}]                    | [{module(), atom(), arity() | [term()],[{atom(), term()}]} | {function(), [term()], [{atom(), term()}]}] disconnect_node( Node() ). 强制断开一个节点的链接 garbage_collect(pid(0,12571,0)). 强制GC make_ref() 通过引用来保证请求和响应包是同一个会话 make_ref() ，它在一个节点的生命周期内几乎是唯一的，2的28次方调用后才会重复 erlang:process_info(pid(0,12571,0)). 查看进程的详细信息 binary_part(Subject, PosLen) -> binary(). binary_part(Subject, Start, Length) -> binary(). binary_part( <<1,2,3,4,5>>, {0,2} ). -> <<1,2>>. exit(whereis(Regname), kill). 杀进程 ```