PR #1672: Optimize StrJoin with tuple without user defined formatter

Imported from GitHub PR https://github.com/abseil/abseil-cpp/pull/1672

https://github.com/abseil/abseil-cpp/discussions/1671

Merge ddcbb2466b2c9c4048d60be7e58cf47f935c257d into eba8db7b

Merging this change closes #1672

COPYBARA_INTEGRATE_REVIEW=https://github.com/abseil/abseil-cpp/pull/1672 from MBkkt:optimize-str-join ddcbb2466b2c9c4048d60be7e58cf47f935c257d
PiperOrigin-RevId: 633988391
Change-Id: I2b3904211a29de3a768fb90a7fc106d7ff6c03e7

absl/strings/internal/str_join_internal.h

@@ -33,6 +33,7 @@
 
 #include <cstdint>
 #include <cstring>
+#include <initializer_list>
 #include <iterator>
 #include <limits>
 #include <memory>
@@ -321,6 +322,15 @@ std::string JoinRange(const Range& range, absl::string_view separator) {
   return JoinRange(begin(range), end(range), separator);
 }
 
+template <typename Tuple, std::size_t... I>
+std::string JoinTuple(const Tuple& value, absl::string_view separator,
+                      std::index_sequence<I...>) {
+  return JoinRange(
+      std::initializer_list<absl::string_view>{
+          static_cast<const AlphaNum&>(std::get<I>(value)).Piece()...},
+      separator);
+}
+
 }  // namespace strings_internal
 ABSL_NAMESPACE_END
 }  // namespace absl

absl/strings/str_join.h

@@ -291,7 +291,8 @@ inline std::string StrJoin(std::initializer_list<absl::string_view> il,
 template <typename... T>
 std::string StrJoin(const std::tuple<T...>& value,
                     absl::string_view separator) {
-  return strings_internal::JoinAlgorithm(value, separator, AlphaNumFormatter());
+  return strings_internal::JoinTuple(value, separator,
+                                     std::index_sequence_for<T...>{});
 }
 
 ABSL_NAMESPACE_END

absl/strings/str_join_benchmark.cc

@@ -16,6 +16,7 @@
 #include "absl/strings/str_join.h"
 
 #include <string>
+#include <tuple>
 #include <vector>
 #include <utility>
 
@@ -94,4 +95,13 @@ BENCHMARK(BM_JoinStreamable)
     ->ArgPair(16, 256)
     ->ArgPair(256, 256);
 
+void BM_JoinTuple(benchmark::State& state) {
+  for (auto _ : state) {
+    std::string s =
+        absl::StrJoin(std::make_tuple(123456789, 987654321, 24680, 13579), "/");
+    benchmark::DoNotOptimize(s);
+  }
+}
+BENCHMARK(BM_JoinTuple);
+
 }  // namespace