Add a template gadget to detect whether a type supports the ostream operator.
I.e. for a type `Example`, if
```
std::ostream& operator<<(std::ostream&, const Example&);
```
is declared, `absl::HasOstreamOperator<Example>::value` is `true`.
PiperOrigin-RevId: 574637891
Change-Id: I123d8f35a6e3ea894745133f7d81b1610fb475d5
diff --git a/CMake/AbseilDll.cmake b/CMake/AbseilDll.cmake
index ecd2d80..1177d5d 100644
--- a/CMake/AbseilDll.cmake
+++ b/CMake/AbseilDll.cmake
@@ -307,6 +307,7 @@
"strings/internal/stringify_sink.h"
"strings/internal/stringify_sink.cc"
"strings/has_absl_stringify.h"
+ "strings/has_ostream_operator.h"
"strings/match.cc"
"strings/match.h"
"strings/numbers.cc"
diff --git a/absl/strings/BUILD.bazel b/absl/strings/BUILD.bazel
index 3727349..a3ef3ae 100644
--- a/absl/strings/BUILD.bazel
+++ b/absl/strings/BUILD.bazel
@@ -194,6 +194,31 @@
visibility = ["//visibility:private"],
deps = [
":strings",
+ "//absl/types:optional",
+ "@com_google_googletest//:gtest",
+ "@com_google_googletest//:gtest_main",
+ ],
+)
+
+cc_library(
+ name = "has_ostream_operator",
+ hdrs = ["has_ostream_operator.h"],
+ copts = ABSL_DEFAULT_COPTS,
+ linkopts = ABSL_DEFAULT_LINKOPTS,
+ deps = [
+ "//absl/base:config",
+ ],
+)
+
+cc_test(
+ name = "has_ostream_operator_test",
+ size = "small",
+ srcs = ["has_ostream_operator_test.cc"],
+ copts = ABSL_TEST_COPTS,
+ visibility = ["//visibility:private"],
+ deps = [
+ ":has_ostream_operator",
+ "//absl/types:optional",
"@com_google_googletest//:gtest",
"@com_google_googletest//:gtest_main",
],
diff --git a/absl/strings/CMakeLists.txt b/absl/strings/CMakeLists.txt
index f470ff5..b129096 100644
--- a/absl/strings/CMakeLists.txt
+++ b/absl/strings/CMakeLists.txt
@@ -103,6 +103,18 @@
PUBLIC
)
+absl_cc_library(
+ NAME
+ has_ostream_operator
+ HDRS
+ "has_ostream_operator.h"
+ COPTS
+ ${ABSL_DEFAULT_COPTS}
+ DEPS
+ absl::config
+ PUBLIC
+)
+
# Internal-only target, do not depend on directly.
absl_cc_library(
NAME
@@ -162,12 +174,26 @@
COPTS
${ABSL_TEST_COPTS}
DEPS
+ absl::optional
absl::strings
GTest::gmock_main
)
absl_cc_test(
NAME
+ has_ostream_operator_test
+ SRCS
+ "has_ostream_operator_test.cc"
+ COPTS
+ ${ABSL_TEST_COPTS}
+ DEPS
+ absl::has_ostream_operator
+ absl::optional
+ GTest::gmock_main
+)
+
+absl_cc_test(
+ NAME
ascii_test
SRCS
"ascii_test.cc"
diff --git a/absl/strings/has_absl_stringify_test.cc b/absl/strings/has_absl_stringify_test.cc
index e9915c6..59e7e1d 100644
--- a/absl/strings/has_absl_stringify_test.cc
+++ b/absl/strings/has_absl_stringify_test.cc
@@ -17,6 +17,7 @@
#include <string>
#include "gtest/gtest.h"
+#include "absl/types/optional.h"
namespace {
@@ -32,6 +33,8 @@
EXPECT_FALSE(absl::HasAbslStringify<std::string>::value);
EXPECT_FALSE(absl::HasAbslStringify<TypeWithoutAbslStringify>::value);
EXPECT_TRUE(absl::HasAbslStringify<TypeWithAbslStringify>::value);
+ EXPECT_FALSE(
+ absl::HasAbslStringify<absl::optional<TypeWithAbslStringify>>::value);
}
} // namespace
diff --git a/absl/strings/has_ostream_operator.h b/absl/strings/has_ostream_operator.h
new file mode 100644
index 0000000..156ffc7
--- /dev/null
+++ b/absl/strings/has_ostream_operator.h
@@ -0,0 +1,42 @@
+// Copyright 2023 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_STRINGS_HAS_OSTREAM_OPERATOR_H_
+#define ABSL_STRINGS_HAS_OSTREAM_OPERATOR_H_
+
+#include <ostream>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// Detects if type `T` supports streaming to `std::ostream`s with `operator<<`.
+
+template <typename T, typename = void>
+struct HasOstreamOperator : std::false_type {};
+
+template <typename T>
+struct HasOstreamOperator<
+ T, std::enable_if_t<std::is_same<
+ std::ostream&, decltype(std::declval<std::ostream&>()
+ << std::declval<const T&>())>::value>>
+ : std::true_type {};
+
+ABSL_NAMESPACE_END
+} // namespace absl
+
+#endif // ABSL_STRINGS_HAS_OSTREAM_OPERATOR_H_
diff --git a/absl/strings/has_ostream_operator_test.cc b/absl/strings/has_ostream_operator_test.cc
new file mode 100644
index 0000000..9ef4136
--- /dev/null
+++ b/absl/strings/has_ostream_operator_test.cc
@@ -0,0 +1,41 @@
+// Copyright 2023 The Abseil Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/strings/has_ostream_operator.h"
+
+#include <ostream>
+#include <string>
+
+#include "gtest/gtest.h"
+#include "absl/types/optional.h"
+
+namespace {
+
+struct TypeWithoutOstreamOp {};
+
+struct TypeWithOstreamOp {
+ friend std::ostream& operator<<(std::ostream& os, const TypeWithOstreamOp&) {
+ return os;
+ }
+};
+
+TEST(HasOstreamOperatorTest, Works) {
+ EXPECT_TRUE(absl::HasOstreamOperator<int>::value);
+ EXPECT_TRUE(absl::HasOstreamOperator<std::string>::value);
+ EXPECT_FALSE(absl::HasOstreamOperator<absl::optional<int>>::value);
+ EXPECT_FALSE(absl::HasOstreamOperator<TypeWithoutOstreamOp>::value);
+ EXPECT_TRUE(absl::HasOstreamOperator<TypeWithOstreamOp>::value);
+}
+
+} // namespace
