From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp48.i.mail.ru (smtp48.i.mail.ru [94.100.177.108]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dev.tarantool.org (Postfix) with ESMTPS id 6AFEC469710 for ; Fri, 15 May 2020 00:28:40 +0300 (MSK) References: <22a830fb9d2dbc3883b9710d36ab88c638101002.1589240704.git.v.shpilevoy@tarantool.org> <20200513123145.GA16814@tarantool.org> <06c4d5d9-db84-4043-0d7a-81c0320b6663@tarantool.org> <20200514023242.GE18509@tarantool.org> From: Vladislav Shpilevoy Message-ID: <27e7c364-8242-6c7b-c38c-0ad578e4977e@tarantool.org> Date: Thu, 14 May 2020 23:28:38 +0200 MIME-Version: 1.0 In-Reply-To: <20200514023242.GE18509@tarantool.org> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit Subject: Re: [Tarantool-patches] [PATCH 4/5] error: provide MP_ERROR extension serializer List-Id: Tarantool development patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Nikita Pettik Cc: tarantool-patches@dev.tarantool.org Hi! Thanks for the review! >>> /** >>> * MP_ERROR extension string serializer. >>> * There are two applications for string serialization - into a >>> * buffer, and into a file. Structure of both is exactly the same >>> * except for the copying/writing itself. To avoid code >>> * duplication the code is templated and expects some macros to do >>> * the actual output. >>> */ >> This is basically a C template. The same as bps tree, rb tree, mhash. But >> located in the same source file which needs it. Since this is not a common >> enough feature to move it to a separate place. >> >> I include self with pre-declared macros MP_ERROR_PRINT_DEFINITION. When it >> is defined, the file skips everything except the 3 functions in the end: >> mp_print_error_one(), mp_print_error_stack(), mp_print_error(). > > A-ha, it is what I missed. But personally I would anyway move these > macros/functions to a separate file. It would definitely cut extra > questions and would make code cleaner (IMHO) (I bet anybody who > sees '#include __FILE__' for the first time is like 'WTF?!'). But! How cool the self inclusion is 😎. If someone would wrap these things into neat macros, it could be a useful tool to replace C++ templates, which are the only real problem on the way of getting rid of C++ from the code base. For example, tuple comparators heavily depend on templates, and their move to separate files is hardly possible - they depend on tuple_compare.cc internals too much. Jokes aside, self inclusion solves one important issue - non templated dependencies. If I move the templates to a different file, it needs to include "mp_error.h", at least for MP_ERROR_* enum constants. Strictly speaking. Also it needs MessagePack headers, and can't use any mp_error.cc internal functions even though these templates *are* internal too. >> The skip uses mere #ifdef MP_ERROR_PRINT_DEFINITION to understand, that >> currently the file is being included into self to customize the error >> printers. So all is skipped except them. >> >> I include the file twice, but with different parameters. Like if I would >> customize one template with two parameter sets in C++. First inclusion >> turns >> >> mp_print_error_one(), mp_print_error_stack(), mp_print_error() >> >> into >> >> mp_snprint_error_one(), mp_snprint_error_stack(), mp_snprint_error() >> >> and snprintf() calls inside. The second inclusion turns the functions into >> >> mp_fprint_error_one(), mp_fprint_error_stack(), mp_fprint_error() >> >> and fprintf() calls inside. >> >> I tried to extend the comment. > > You gave cool explanation right in this message. Why not copy it to > the source file? Because it is too common. Can't put it in just one place, since the mentioned things are spread on the file. I tried to split it in parts and put them where they belong. In addition to the comment I added previously. diff --git a/src/box/mp_error.cc b/src/box/mp_error.cc index a4a4ccaca..23a74d0a9 100644 --- a/src/box/mp_error.cc +++ b/src/box/mp_error.cc @@ -28,6 +28,11 @@ * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ +/** + * When this macros is defined, it means the file included self in + * order to customize some templates. Skip everything except them + * then. + */ #ifndef MP_ERROR_PRINT_DEFINITION #include "box/mp_error.h" @@ -556,6 +561,11 @@ error_unpack_unsafe(const char **data) return err; } +/** + * Include this file into self with a few template parameters + * to create mp_snprint_error() and mp_fprint_error() functions + * and their helpers from a printer template. + */ #define MP_ERROR_PRINT_DEFINITION #define MP_PRINT_FUNC snprintf #define MP_PRINT_SUFFIX snprint @@ -675,6 +685,11 @@ mp_print_error_stack(MP_PRINT_ARGS_DECL, const char **data, int depth) return total; } +/** + * The main printer template. Depending on template parameters it + * is turned into mp_snprint_error() with snprintf() semantics or + * into mp_fprint_error() with fprintf() semantics. + */ int mp_print_error(MP_PRINT_ARGS_DECL, const char **data, int depth) {