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-rw-r--r--absl/flags/flag.h45
1 files changed, 33 insertions, 12 deletions
diff --git a/absl/flags/flag.h b/absl/flags/flag.h
index 326fb8ee..62e73f84 100644
--- a/absl/flags/flag.h
+++ b/absl/flags/flag.h
@@ -29,6 +29,8 @@
#ifndef ABSL_FLAGS_FLAG_H_
#define ABSL_FLAGS_FLAG_H_
+#include <type_traits>
+
#include "absl/base/attributes.h"
#include "absl/base/casts.h"
#include "absl/flags/config.h"
@@ -181,23 +183,42 @@ class Flag {
//
// // FLAGS_firstname is a Flag of type `std::string`
// std::string first_name = absl::GetFlag(FLAGS_firstname);
-template <typename T>
+template <typename T,
+ typename std::enable_if<
+ !flags_internal::IsAtomicFlagTypeTrait<T>::value, int>::type = 0>
ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag) {
-#define ABSL_FLAGS_INTERNAL_LOCK_FREE_VALIDATE(BIT) \
- static_assert( \
- !std::is_same<T, BIT>::value, \
- "Do not specify explicit template parameters to absl::GetFlag");
- ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(ABSL_FLAGS_INTERNAL_LOCK_FREE_VALIDATE)
-#undef ABSL_FLAGS_INTERNAL_LOCK_FREE_VALIDATE
-
return flag.Get();
}
+// We want to validate the type mismatch between type definition and
+// declaration. The lock-free implementation does not allow us to do it,
+// so in debug builds we always use the slower implementation, which always
+// validates the type.
+#ifndef NDEBUG
+template <typename T,
+ typename std::enable_if<
+ flags_internal::IsAtomicFlagTypeTrait<T>::value, int>::type = 0>
+ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag) {
+ return flag.Get();
+}
+#else
// Overload for `GetFlag()` for types that support lock-free reads.
-#define ABSL_FLAGS_INTERNAL_LOCK_FREE_EXPORT(T) \
- ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag);
-ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(ABSL_FLAGS_INTERNAL_LOCK_FREE_EXPORT)
-#undef ABSL_FLAGS_INTERNAL_LOCK_FREE_EXPORT
+template <typename T,
+ typename std::enable_if<
+ flags_internal::IsAtomicFlagTypeTrait<T>::value, int>::type = 0>
+ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag) {
+ // T might not be default constructible.
+ union U {
+ T value;
+ U() {}
+ };
+ U result;
+ if (flag.AtomicGet(&result.value)) {
+ return result.value;
+ }
+ return flag.Get();
+}
+#endif
// SetFlag()
//