// // Copyright 2019 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 // // https://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_FLAGS_INTERNAL_COMMANDLINEFLAG_H_ #define ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_ #include <memory> #include <string> #include "absl/base/config.h" #include "absl/base/internal/fast_type_id.h" #include "absl/base/macros.h" #include "absl/strings/string_view.h" #include "absl/types/optional.h" namespace absl { ABSL_NAMESPACE_BEGIN namespace flags_internal { // An alias for flag fast type id. This value identifies the flag value type // simialarly to typeid(T), without relying on RTTI being available. In most // cases this id is enough to uniquely identify the flag's value type. In a few // cases we'll have to resort to using actual RTTI implementation if it is // available. using FlagFastTypeId = base_internal::FastTypeIdType; // Options that control SetCommandLineOptionWithMode. enum FlagSettingMode { // update the flag's value unconditionally (can call this multiple times). SET_FLAGS_VALUE, // update the flag's value, but *only if* it has not yet been updated // with SET_FLAGS_VALUE, SET_FLAG_IF_DEFAULT, or "FLAGS_xxx = nondef". SET_FLAG_IF_DEFAULT, // set the flag's default value to this. If the flag has not been updated // yet (via SET_FLAGS_VALUE, SET_FLAG_IF_DEFAULT, or "FLAGS_xxx = nondef") // change the flag's current value to the new default value as well. SET_FLAGS_DEFAULT }; // Options that control ParseFrom: Source of a value. enum ValueSource { // Flag is being set by value specified on a command line. kCommandLine, // Flag is being set by value specified in the code. kProgrammaticChange, }; // Handle to FlagState objects. Specific flag state objects will restore state // of a flag produced this flag state from method CommandLineFlag::SaveState(). class FlagStateInterface { public: virtual ~FlagStateInterface(); // Restores the flag originated this object to the saved state. virtual void Restore() const = 0; }; // Holds all information for a flag. class CommandLineFlag { public: constexpr CommandLineFlag() = default; // Not copyable/assignable. CommandLineFlag(const CommandLineFlag&) = delete; CommandLineFlag& operator=(const CommandLineFlag&) = delete; // Non-polymorphic access methods. // Return true iff flag has type T. template <typename T> inline bool IsOfType() const { return TypeId() == base_internal::FastTypeId<T>(); } // Attempts to retrieve the flag value. Returns value on success, // absl::nullopt otherwise. template <typename T> absl::optional<T> TryGet() const { if (IsRetired() || !IsOfType<T>()) { return absl::nullopt; } // Implementation notes: // // We are wrapping a union around the value of `T` to serve three purposes: // // 1. `U.value` has correct size and alignment for a value of type `T` // 2. The `U.value` constructor is not invoked since U's constructor does // not do it explicitly. // 3. The `U.value` destructor is invoked since U's destructor does it // explicitly. This makes `U` a kind of RAII wrapper around non default // constructible value of T, which is destructed when we leave the // scope. We do need to destroy U.value, which is constructed by // CommandLineFlag::Read even though we left it in a moved-from state // after std::move. // // All of this serves to avoid requiring `T` being default constructible. union U { T value; U() {} ~U() { value.~T(); } }; U u; Read(&u.value); return std::move(u.value); } // Polymorphic access methods // Returns name of this flag. virtual absl::string_view Name() const = 0; // Returns name of the file where this flag is defined. virtual std::string Filename() const = 0; // Returns help message associated with this flag. virtual std::string Help() const = 0; // Returns true iff this object corresponds to retired flag. virtual bool IsRetired() const; virtual std::string DefaultValue() const = 0; virtual std::string CurrentValue() const = 0; // Sets the value of the flag based on specified string `value`. If the flag // was successfully set to new value, it returns true. Otherwise, sets `error` // to indicate the error, leaves the flag unchanged, and returns false. bool ParseFrom(absl::string_view value, std::string* error); protected: ~CommandLineFlag() = default; private: friend class PrivateHandleAccessor; // Sets the value of the flag based on specified string `value`. If the flag // was successfully set to new value, it returns true. Otherwise, sets `error` // to indicate the error, leaves the flag unchanged, and returns false. There // are three ways to set the flag's value: // * Update the current flag value // * Update the flag's default value // * Update the current flag value if it was never set before // The mode is selected based on `set_mode` parameter. virtual bool ParseFrom(absl::string_view value, flags_internal::FlagSettingMode set_mode, flags_internal::ValueSource source, std::string* error) = 0; // Returns id of the flag's value type. virtual FlagFastTypeId TypeId() const = 0; // Interface to save flag to some persistent state. Returns current flag state // or nullptr if flag does not support saving and restoring a state. virtual std::unique_ptr<FlagStateInterface> SaveState() = 0; // Copy-construct a new value of the flag's type in a memory referenced by // the dst based on the current flag's value. virtual void Read(void* dst) const = 0; // To be deleted. Used to return true if flag's current value originated from // command line. virtual bool IsSpecifiedOnCommandLine() const = 0; // Validates supplied value usign validator or parseflag routine virtual bool ValidateInputValue(absl::string_view value) const = 0; // Checks that flags default value can be converted to string and back to the // flag's value type. virtual void CheckDefaultValueParsingRoundtrip() const = 0; }; } // namespace flags_internal ABSL_NAMESPACE_END } // namespace absl #endif // ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_