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authorGravatar Abseil Team <absl-team@google.com>2022-01-31 09:50:11 -0800
committerGravatar Derek Mauro <dmauro@google.com>2022-01-31 15:27:28 -0500
commit63d26fad49463561c2427a45aab283938ade10d9 (patch)
tree1b23aaa7fe57d425fc28240fab059eecf20f9ebb
parent940c06c25d2953f44310b68eb8aab6114dba11fb (diff)
Export of internal Abseil changes
-- c475e8ac1ea163248415e7d4bdc05e3c47dd8f3d by Derek Mauro <dmauro@google.com>: Replace absl::bit_cast with std::bit_cast in C++20 Remove the deprecated implementation that is less-strict than the standard, and also relies on undefined behavior PiperOrigin-RevId: 425391711 -- dc97c996aed85161f0e490baafd3ed851e8bea9d by Abseil Team <absl-team@google.com>: Add enum example for ABSL_DEPRECATED() PiperOrigin-RevId: 425311634 GitOrigin-RevId: c475e8ac1ea163248415e7d4bdc05e3c47dd8f3d Change-Id: Id8f159b37fe3f3cace6ab7bce08daf9888c44bcf
-rw-r--r--absl/base/attributes.h4
-rw-r--r--absl/base/casts.h78
2 files changed, 33 insertions, 49 deletions
diff --git a/absl/base/attributes.h b/absl/base/attributes.h
index 4ab6fa27..91aabffe 100644
--- a/absl/base/attributes.h
+++ b/absl/base/attributes.h
@@ -656,6 +656,10 @@
// ABSL_DEPRECATED("Use DoThat() instead")
// void DoThis();
//
+// enum FooEnum {
+// kBar ABSL_DEPRECATED("Use kBaz instead"),
+// };
+//
// Every usage of a deprecated entity will trigger a warning when compiled with
// clang's `-Wdeprecated-declarations` option. This option is turned off by
// default, but the warnings will be reported by clang-tidy.
diff --git a/absl/base/casts.h b/absl/base/casts.h
index bf100efa..b99adb06 100644
--- a/absl/base/casts.h
+++ b/absl/base/casts.h
@@ -29,6 +29,10 @@
#include <type_traits>
#include <utility>
+#if defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+#include <bit> // For std::bit_cast.
+#endif // defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+
#include "absl/base/internal/identity.h"
#include "absl/base/macros.h"
#include "absl/meta/type_traits.h"
@@ -36,23 +40,6 @@
namespace absl {
ABSL_NAMESPACE_BEGIN
-namespace internal_casts {
-
-template <class Dest, class Source>
-struct is_bitcastable
- : std::integral_constant<
- bool,
- sizeof(Dest) == sizeof(Source) &&
- type_traits_internal::is_trivially_copyable<Source>::value &&
- type_traits_internal::is_trivially_copyable<Dest>::value
-#if !ABSL_HAVE_BUILTIN(__builtin_bit_cast)
- && std::is_default_constructible<Dest>::value
-#endif
- > {
-};
-
-} // namespace internal_casts
-
// implicit_cast()
//
// Performs an implicit conversion between types following the language
@@ -123,7 +110,7 @@ constexpr To implicit_cast(typename absl::internal::identity_t<To> to) {
// floating point value:
//
// float f = 3.14159265358979;
-// int i = bit_cast<int32_t>(f);
+// int i = bit_cast<int>(f);
// // i = 0x40490fdb
//
// Reinterpreting and accessing a value directly as a different type (as shown
@@ -151,48 +138,41 @@ constexpr To implicit_cast(typename absl::internal::identity_t<To> to) {
// introducing this undefined behavior (since the original value is never
// accessed in the wrong way).
//
-// NOTE: The requirements here are more strict than the bit_cast of standard
-// proposal P0476 when __builtin_bit_cast is not available.
-// Specifically, this implementation also requires `Dest` to be
-// default-constructible.
-template <
- typename Dest, typename Source,
- typename std::enable_if<internal_casts::is_bitcastable<Dest, Source>::value,
- int>::type = 0>
+// The requirements of `absl::bit_cast` are more strict than that of
+// `std::bit_cast` unless compiler support is available. Specifically, without
+// compiler support, this implementation also requires `Dest` to be
+// default-constructible. In C++20, `absl::bit_cast` is replaced by
+// `std::bit_cast`.
+#if defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+
+using std::bit_cast;
+
+#else // defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+
+template <typename Dest, typename Source,
+ typename std::enable_if<
+ sizeof(Dest) == sizeof(Source) &&
+ type_traits_internal::is_trivially_copyable<Source>::value &&
+ type_traits_internal::is_trivially_copyable<Dest>::value
+#if !ABSL_HAVE_BUILTIN(__builtin_bit_cast)
+ && std::is_default_constructible<Dest>::value
+#endif // !ABSL_HAVE_BUILTIN(__builtin_bit_cast)
+ ,
+ int>::type = 0>
#if ABSL_HAVE_BUILTIN(__builtin_bit_cast)
inline constexpr Dest bit_cast(const Source& source) {
return __builtin_bit_cast(Dest, source);
}
-#else
+#else // ABSL_HAVE_BUILTIN(__builtin_bit_cast)
inline Dest bit_cast(const Source& source) {
Dest dest;
memcpy(static_cast<void*>(std::addressof(dest)),
static_cast<const void*>(std::addressof(source)), sizeof(dest));
return dest;
}
-#endif
-
-// NOTE: This overload is only picked if the requirements of bit_cast are
-// not met. It is therefore UB, but is provided temporarily as previous
-// versions of this function template were unchecked. Do not use this in
-// new code.
-template <
- typename Dest, typename Source,
- typename std::enable_if<
- !internal_casts::is_bitcastable<Dest, Source>::value,
- int>::type = 0>
-ABSL_DEPRECATED(
- "absl::bit_cast type requirements were violated. Update the types "
- "being used such that they are the same size and are both "
- "TriviallyCopyable.")
-inline Dest bit_cast(const Source& source) {
- static_assert(sizeof(Dest) == sizeof(Source),
- "Source and destination types should have equal sizes.");
+#endif // ABSL_HAVE_BUILTIN(__builtin_bit_cast)
- Dest dest;
- memcpy(&dest, &source, sizeof(dest));
- return dest;
-}
+#endif // defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
ABSL_NAMESPACE_END
} // namespace absl