| // |
| // 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 <stddef.h> |
| #include <stdint.h> |
| |
| #include <memory> |
| #include <string> |
| #include <typeinfo> |
| |
| #include "absl/base/config.h" |
| #include "absl/base/macros.h" |
| #include "absl/flags/config.h" |
| #include "absl/flags/marshalling.h" |
| #include "absl/strings/string_view.h" |
| #include "absl/types/optional.h" |
| |
| namespace absl { |
| ABSL_NAMESPACE_BEGIN |
| namespace flags_internal { |
| |
| // An alias for flag static type id. Values of type identify the flag value type |
| // simialarly to typeid(T), but 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 FlagStaticTypeId = void* (*)(); |
| |
| // Address of this function template is used in current implementation as a flag |
| // static type id. |
| template <typename T> |
| void* FlagStaticTypeIdGen() { |
| #if defined(ABSL_FLAGS_INTERNAL_HAS_RTTI) |
| return const_cast<std::type_info*>(&typeid(T)); |
| #else |
| return nullptr; |
| #endif |
| } |
| |
| // 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 SetFromString: 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() == &flags_internal::FlagStaticTypeIdGen<T>; |
| } |
| |
| // Attempts to retrieve the flag value. Returns value on success, |
| // absl::nullopt otherwise. |
| template <typename T> |
| absl::optional<T> Get() 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 name of the flag's value type for some built-in types or empty |
| // std::string. |
| virtual absl::string_view Typename() 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 { return false; } |
| // Returns true iff this is a handle to an Abseil Flag. |
| virtual bool IsAbseilFlag() const { return true; } |
| // Returns id of the flag's value type. |
| virtual FlagStaticTypeId TypeId() const = 0; |
| virtual bool IsModified() const = 0; |
| virtual bool IsSpecifiedOnCommandLine() const = 0; |
| virtual std::string DefaultValue() const = 0; |
| virtual std::string CurrentValue() const = 0; |
| |
| // Interfaces to operate on validators. |
| virtual bool ValidateInputValue(absl::string_view value) 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; |
| |
| // Sets the value of the flag based on specified std::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 SetFromString(absl::string_view value, |
| flags_internal::FlagSettingMode set_mode, |
| flags_internal::ValueSource source, |
| std::string* error) = 0; |
| |
| // Checks that flags default value can be converted to std::string and back to the |
| // flag's value type. |
| virtual void CheckDefaultValueParsingRoundtrip() const = 0; |
| |
| protected: |
| ~CommandLineFlag() = default; |
| |
| private: |
| // 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; |
| }; |
| |
| // This macro is the "source of truth" for the list of supported flag built-in |
| // types. |
| #define ABSL_FLAGS_INTERNAL_BUILTIN_TYPES(A) \ |
| A(bool) \ |
| A(short) \ |
| A(unsigned short) \ |
| A(int) \ |
| A(unsigned int) \ |
| A(long) \ |
| A(unsigned long) \ |
| A(long long) \ |
| A(unsigned long long) \ |
| A(double) \ |
| A(float) \ |
| A(std::string) \ |
| A(std::vector<std::string>) |
| |
| } // namespace flags_internal |
| ABSL_NAMESPACE_END |
| } // namespace absl |
| |
| #endif // ABSL_FLAGS_INTERNAL_COMMANDLINEFLAG_H_ |