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efee2e57e9
Fix #1817 PiperOrigin-RevId: 813902689 Change-Id: Ic3508c02d5ed2e7dc220cdf02526680ae0adbbc1
78 lines
2.7 KiB
C++
78 lines
2.7 KiB
C++
//
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// Copyright 2019 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// -----------------------------------------------------------------------------
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// File: declare.h
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// -----------------------------------------------------------------------------
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//
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// This file defines the ABSL_DECLARE_FLAG macro, allowing you to declare an
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// `absl::Flag` for use within a translation unit. You should place this
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// declaration within the header file associated with the .cc file that defines
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// and owns the `Flag`.
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#ifndef ABSL_FLAGS_DECLARE_H_
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#define ABSL_FLAGS_DECLARE_H_
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#include "absl/base/config.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace flags_internal {
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// absl::Flag<T> represents a flag of type 'T' created by ABSL_FLAG.
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template <typename T>
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class Flag;
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} // namespace flags_internal
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// Flag
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//
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// Forward declaration of the `absl::Flag` type for use in defining the macro.
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template <typename T>
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using Flag = flags_internal::Flag<T>;
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ABSL_NAMESPACE_END
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} // namespace absl
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// ABSL_DECLARE_FLAG()
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//
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// This macro is a convenience for declaring use of an `absl::Flag` within a
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// translation unit. This macro should be used within a header file to
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// declare usage of the flag within any .cc file including that header file.
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//
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// The ABSL_DECLARE_FLAG(type, name) macro expands to:
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//
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// extern absl::Flag<type> FLAGS_name;
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#define ABSL_DECLARE_FLAG(type, name) ABSL_DECLARE_FLAG_INTERNAL(type, name)
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// Internal implementation of ABSL_DECLARE_FLAG to allow macro expansion of its
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// arguments. Clients must use ABSL_DECLARE_FLAG instead.
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//
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// The non-MSVC implementation declares the flag twice. This is to allow
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// applying attributes to the second declaration. However, this causes a
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// compile error (C4273) in MSVC if a `__declspec` is prepended to the macro.
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#if defined(_MSC_VER)
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#define ABSL_DECLARE_FLAG_INTERNAL(type, name) \
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extern absl::Flag<type> FLAGS_##name
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#else
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#define ABSL_DECLARE_FLAG_INTERNAL(type, name) \
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extern absl::Flag<type> FLAGS_##name; \
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namespace absl /* block flags in namespaces */ {} \
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/* second redeclaration is to allow applying attributes */ \
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extern absl::Flag<type> FLAGS_##name
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#endif // _MSC_VER
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#endif // ABSL_FLAGS_DECLARE_H_
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