add: [log] a simple implementation to be optimized

CMakeLists.txt

@@ -66,7 +66,7 @@ endif()
 if (LIBIPC_BUILD_BENCHMARK)
   set(BENCHMARK_ENABLE_TESTING OFF)
   add_subdirectory(3rdparty/benchmark)
-  # add_subdirectory(benchmark)
+  add_subdirectory(benchmark)
 endif()
 
 install(

benchmark/benchmark_log.cpp

@@ -0,0 +1,17 @@
+
+#include "benchmark/benchmark.h"
+
+#include "libimp/log.h"
+
+namespace {
+
+void BM_imp_log_gripper(benchmark::State& state) {
+  imp::log::gripper log {{}, __func__};
+  for (auto _ : state) {
+    log.info("hello log.");
+  }
+}
+
+} // namespace
+
+BENCHMARK(BM_imp_log_gripper);

include/libimp/log.h

@@ -8,8 +8,10 @@
 
 #include <string>
 #include <type_traits>
+#include <chrono>
 
 #include "fmt/format.h"
+#include "fmt/chrono.h"
 
 #include "libimp/def.h"
 #include "libimp/detect_plat.h"
@@ -88,22 +90,6 @@ public:
   }
 };
 
-class prefix {
-  std::string px_;
-
-public:
-  template <typename... A>
-  prefix(A &&... args) {
-    LIBIMP_UNUSED auto unfold = {
-      0, ((px_ += ::fmt::format("[{}]", std::forward<A>(args))), 0)...
-    };
-  }
-
-  operator std::string() const noexcept {
-    return px_;
-  }
-};
-
 } // namespace detail_log
 
 class LIBIMP_EXPORT log_printer {
@@ -139,6 +125,32 @@ std::string fmt(Fmt &&ft, A &&... args) {
   return ::fmt::format(std::forward<Fmt>(ft), std::forward<A>(args)...);
 }
 
-} // namespace log
+class LIBIMP_EXPORT gripper {
+  log_printer printer_;
+  char const *func_;
 
+  gripper &output(void (log_printer::*out_fn)(std::string &&), char type, std::string &&log_str) {
+    auto tm = std::chrono::system_clock::now();
+    auto ms = std::chrono::time_point_cast<std::chrono::milliseconds>(tm).time_since_epoch().count() % 1000;
+    auto px = fmt("[{}][{:%Y-%m-%d %H:%M:%S}.{:03}][{}]\n", type, tm, ms, func_);
+    (printer_.*out_fn)(std::move(px += std::move(log_str)));
+    return *this;
+  }
+
+public:
+  gripper(log_printer printer, char const *func) noexcept 
+    : printer_(printer)
+    , func_   (func) {}
+
+  template <typename Fmt, typename... A>
+  gripper &info(Fmt &&ft, A &&... args) {
+    return output(&log_printer::info, 'I', fmt(std::forward<Fmt>(ft), std::forward<A>(args)...));
+  }
+  template <typename Fmt, typename... A>
+  gripper &error(Fmt &&ft, A &&... args) {
+    return output(&log_printer::error, 'E', fmt(std::forward<Fmt>(ft), std::forward<A>(args)...));
+  }
+};
+
+} // namespace log
 LIBIMP_NAMESPACE_END_

include/libimp/result.h

@@ -157,7 +157,6 @@ struct fmt::formatter<::LIBIMP_::result<T, D>> {
   constexpr auto parse(format_parse_context& ctx) const {
     return ctx.end();
   }
-
   template <typename FormatContext>
   auto format(::LIBIMP_::result<T, D> r, FormatContext &ctx) {
     return format_to(::LIBIMP_::result<T, D>::default_traits_t::format(r, 

src/libimp/log.cpp

@@ -1,6 +1,6 @@
 
 #include <utility>
-#include <iostream>
+#include <cstdio>
 
 #include "libimp/log.h"
 
@@ -23,11 +23,11 @@ void log_printer::error(std::string && s) {
 log_std_t log_std;
 
 void log_std_t::info(std::string && s) const {
-  std::cout << std::move(s);
+  std::fprintf(stdin, "%s", s.c_str());
 }
 
 void log_std_t::error(std::string && s) const {
-  std::cerr << std::move(s);
+  std::fprintf(stderr, "%s", s.c_str());
 }
 
 LIBIMP_NAMESPACE_END_

test/test_imp_log.cpp

@@ -74,17 +74,7 @@ TEST(log, log_printer) {
   ps.info("hello world\n");
 }
 
-#include <chrono>
-#include <fmt/chrono.h>
-
-TEST(log, prefix) {
-  imp::detail_log::prefix prefix;
-  EXPECT_EQ(std::string{prefix}, "");
-
-  prefix = {"hello", "world"};
-  EXPECT_EQ(std::string{prefix}, "[hello][world]");
-
-  using namespace std::literals::chrono_literals;
-  prefix = {"time", imp::log::fmt("{:%H:%M:%S}", 3h + 15min + 30s)};
-  EXPECT_EQ(std::string{prefix}, "[time][03:15:30]");
+TEST(log, gripper) {
+  imp::log::gripper log {imp::log_std, __func__};
+  log.info("hello");
 }