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//
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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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#ifndef ABSL_FLAGS_INTERNAL_FLAG_H_
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#define ABSL_FLAGS_INTERNAL_FLAG_H_
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#include "absl/flags/internal/commandlineflag.h"
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#include "absl/flags/internal/registry.h"
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namespace absl {
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namespace flags_internal {
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// This is "unspecified" implementation of absl::Flag<T> type.
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template <typename T>
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class Flag {
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public:
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constexpr Flag(const char* name, const flags_internal::HelpGenFunc help_gen,
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const char* filename,
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const flags_internal::FlagMarshallingOpFn marshalling_op,
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const flags_internal::InitialValGenFunc initial_value_gen)
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: internal(name, flags_internal::HelpText::FromFunctionPointer(help_gen),
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filename, &flags_internal::FlagOps<T>, marshalling_op,
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initial_value_gen,
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/*retired_arg=*/false, /*def_arg=*/nullptr,
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/*cur_arg=*/nullptr) {}
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// Not copyable/assignable.
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Flag(const Flag<T>&) = delete;
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Flag<T>& operator=(const Flag<T>&) = delete;
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absl::string_view Name() const { return internal.Name(); }
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std::string Help() const { return internal.Help(); }
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std::string Filename() const { return internal.Filename(); }
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absl::flags_internal::CommandLineFlag internal;
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void SetCallback(const flags_internal::FlagCallback mutation_callback) {
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internal.SetCallback(mutation_callback);
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}
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private:
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// TODO(rogeeff): add these validations once UnparseFlag invocation is fixed
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// for built-in types and when we cleanup existing code from operating on
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// forward declared types.
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// auto IsCopyConstructible(const T& v) -> decltype(T(v));
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// auto HasAbslParseFlag(absl::string_view in, T* dst, std::string* err)
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// -> decltype(AbslParseFlag(in, dst, err));
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// auto HasAbslUnparseFlag(const T& v) -> decltype(AbslUnparseFlag(v));
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};
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// This class facilitates Flag object registration and tail expression-based
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// flag definition, for example:
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// ABSL_FLAG(int, foo, 42, "Foo help").OnUpdate(NotifyFooWatcher);
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template <typename T, bool do_register>
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class FlagRegistrar {
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public:
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explicit FlagRegistrar(Flag<T>* flag) : flag_(flag) {
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if (do_register) flags_internal::RegisterCommandLineFlag(&flag_->internal);
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}
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FlagRegistrar& OnUpdate(flags_internal::FlagCallback cb) && {
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flag_->SetCallback(cb);
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return *this;
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}
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// Make the registrar "die" gracefully as a bool on a line where registration
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// happens. Registrar objects are intended to live only as temporary.
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operator bool() const { return true; } // NOLINT
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private:
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Flag<T>* flag_; // Flag being registered (not owned).
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};
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// This struct and corresponding overload to MakeDefaultValue are used to
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// facilitate usage of {} as default value in ABSL_FLAG macro.
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struct EmptyBraces {};
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template <typename T>
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T* MakeFromDefaultValue(T t) {
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return new T(std::move(t));
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}
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template <typename T>
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T* MakeFromDefaultValue(EmptyBraces) {
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return new T;
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}
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} // namespace flags_internal
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} // namespace absl
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#endif // ABSL_FLAGS_INTERNAL_FLAG_H_
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