diff options
Diffstat (limited to 'absl/base/internal')
| -rw-r--r-- | absl/base/internal/inline_variable.h | 107 | ||||
| -rw-r--r-- | absl/base/internal/inline_variable_testing.h | 44 |
2 files changed, 151 insertions, 0 deletions
diff --git a/absl/base/internal/inline_variable.h b/absl/base/internal/inline_variable.h new file mode 100644 index 000000000000..f7bb8c56525d --- /dev/null +++ b/absl/base/internal/inline_variable.h @@ -0,0 +1,107 @@ +// Copyright 2017 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 +// +// http://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_BASE_INTERNAL_INLINE_VARIABLE_EMULATION_H_ +#define ABSL_BASE_INTERNAL_INLINE_VARIABLE_EMULATION_H_ + +#include <type_traits> + +#include "absl/base/internal/identity.h" + +// File: +// This file define a macro that allows the creation of or emulation of C++17 +// inline variables based on whether or not the feature is supported. + +//////////////////////////////////////////////////////////////////////////////// +// Macro: ABSL_INTERNAL_INLINE_CONSTEXPR(type, name, init) +// +// Description: +// Expands to the equivalent of an inline constexpr instance of the specified +// `type` and `name`, initialized to the value `init`. If the compiler being +// used is detected as supporting actual inline variables as a language +// feature, then the macro expands to an actual inline variable definition. +// +// Requires: +// `type` is a type that is usable in an extern variable declaration. +// +// Requires: `name` is a valid identifier +// +// Requires: +// `init` is an expression that can be used in the following definition: +// constexpr type name = init; +// +// Usage: +// +// // Equivalent to: `inline constexpr size_t variant_npos = -1;` +// ABSL_INTERNAL_INLINE_CONSTEXPR(size_t, variant_npos, -1); +// +// Differences in implementation: +// For a direct, language-level inline variable, decltype(name) will be the +// type that was specified along with const qualification, whereas for +// emulated inline variables, decltype(name) may be different (in practice +// it will likely be a reference type). +//////////////////////////////////////////////////////////////////////////////// + +#ifdef __cpp_inline_variables + +// Clang's -Wmissing-variable-declarations option erroneously warned that +// inline constexpr objects need to be pre-declared. This has now been fixed, +// but we will need to support this workaround for people building with older +// versions of clang. +// +// Bug: https://bugs.llvm.org/show_bug.cgi?id=35862 +// +// Note: +// identity_t is used here so that the const and name are in the +// appropriate place for pointer types, reference types, function pointer +// types, etc.. +#if defined(__clang__) +#define ABSL_INTERNAL_EXTERN_DECL(type, name) \ + extern const ::absl::internal::identity_t<type> name; +#else // Otherwise, just define the macro to do nothing. +#define ABSL_INTERNAL_EXTERN_DECL(type, name) +#endif // defined(__clang__) + +// See above comment at top of file for details. +#define ABSL_INTERNAL_INLINE_CONSTEXPR(type, name, init) \ + ABSL_INTERNAL_EXTERN_DECL(type, name) \ + inline constexpr ::absl::internal::identity_t<type> name = init + +#else + +// See above comment at top of file for details. +// +// Note: +// identity_t is used here so that the const and name are in the +// appropriate place for pointer types, reference types, function pointer +// types, etc.. +#define ABSL_INTERNAL_INLINE_CONSTEXPR(var_type, name, init) \ + template <class /*AbslInternalDummy*/ = void> \ + struct AbslInternalInlineVariableHolder##name { \ + static constexpr ::absl::internal::identity_t<var_type> kInstance = init; \ + }; \ + \ + template <class AbslInternalDummy> \ + constexpr ::absl::internal::identity_t<var_type> \ + AbslInternalInlineVariableHolder##name<AbslInternalDummy>::kInstance; \ + \ + static constexpr const ::absl::internal::identity_t<var_type>& \ + name = /* NOLINT */ \ + AbslInternalInlineVariableHolder##name<>::kInstance; \ + static_assert(sizeof(void (*)(decltype(name))) != 0, \ + "Silence unused variable warnings.") + +#endif // __cpp_inline_variables + +#endif // ABSL_BASE_INTERNAL_INLINE_VARIABLE_EMULATION_H_ diff --git a/absl/base/internal/inline_variable_testing.h b/absl/base/internal/inline_variable_testing.h new file mode 100644 index 000000000000..a0dd2bb28a40 --- /dev/null +++ b/absl/base/internal/inline_variable_testing.h @@ -0,0 +1,44 @@ +// Copyright 2017 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 +// +// http://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_BASE_INLINE_VARIABLE_TESTING_H_ +#define ABSL_BASE_INLINE_VARIABLE_TESTING_H_ + +#include "absl/base/internal/inline_variable.h" + +namespace absl { +namespace inline_variable_testing_internal { + +struct Foo { + int value = 5; +}; + +ABSL_INTERNAL_INLINE_CONSTEXPR(Foo, inline_variable_foo, {}); +ABSL_INTERNAL_INLINE_CONSTEXPR(Foo, other_inline_variable_foo, {}); + +ABSL_INTERNAL_INLINE_CONSTEXPR(int, inline_variable_int, 5); +ABSL_INTERNAL_INLINE_CONSTEXPR(int, other_inline_variable_int, 5); + +ABSL_INTERNAL_INLINE_CONSTEXPR(void(*)(), inline_variable_fun_ptr, nullptr); + +const Foo& get_foo_a(); +const Foo& get_foo_b(); + +const int& get_int_a(); +const int& get_int_b(); + +} // namespace inline_variable_testing_internal +} // namespace absl + +#endif // ABSL_BASE_INLINE_VARIABLE_TESTING_H_ |