tvl-depot/absl/flags/internal/commandlineflag.h
Abseil Team 564001ae50 Export of internal Abseil changes
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5448463d79c8473d29b6aae62359eaec09e517b0 by Greg Falcon <gfalcon@google.com>:

Rename absl_types_options.h to absl_alternate_options.h, to reflect that we are testing more than just types with this file.

PiperOrigin-RevId: 289099882

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8008a5662d1b27c4ea442575405eb0538f63a636 by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 289097666

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0e9398fae540bdb7dd752245b83456f3784c50ca by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 288985613
GitOrigin-RevId: 5448463d79c8473d29b6aae62359eaec09e517b0
Change-Id: I5bc1ee156294793cacf3acbc447c0ea27ce8af4f
2020-01-10 13:37:41 -05:00

289 lines
9.6 KiB
C++

//
// 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 "absl/base/config.h"
#include "absl/base/macros.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 {
// Type-specific operations, eg., parsing, copying, etc. are provided
// by function specific to that type with a signature matching FlagOpFn.
enum FlagOp {
kDelete,
kClone,
kCopy,
kCopyConstruct,
kSizeof,
kParse,
kUnparse
};
using FlagOpFn = void* (*)(FlagOp, const void*, void*);
using FlagMarshallingOpFn = void* (*)(FlagOp, const void*, void*, void*);
// 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,
};
// The per-type function
template <typename T>
void* FlagOps(FlagOp op, const void* v1, void* v2) {
switch (op) {
case kDelete:
delete static_cast<const T*>(v1);
return nullptr;
case kClone:
return new T(*static_cast<const T*>(v1));
case kCopy:
*static_cast<T*>(v2) = *static_cast<const T*>(v1);
return nullptr;
case kCopyConstruct:
new (v2) T(*static_cast<const T*>(v1));
return nullptr;
case kSizeof:
return reinterpret_cast<void*>(sizeof(T));
default:
return nullptr;
}
}
template <typename T>
void* FlagMarshallingOps(FlagOp op, const void* v1, void* v2, void* v3) {
switch (op) {
case kParse: {
// initialize the temporary instance of type T based on current value in
// destination (which is going to be flag's default value).
T temp(*static_cast<T*>(v2));
if (!absl::ParseFlag<T>(*static_cast<const absl::string_view*>(v1), &temp,
static_cast<std::string*>(v3))) {
return nullptr;
}
*static_cast<T*>(v2) = std::move(temp);
return v2;
}
case kUnparse:
*static_cast<std::string*>(v2) =
absl::UnparseFlag<T>(*static_cast<const T*>(v1));
return nullptr;
default:
return nullptr;
}
}
// Functions that invoke flag-type-specific operations.
inline void Delete(FlagOpFn op, const void* obj) {
op(flags_internal::kDelete, obj, nullptr);
}
inline void* Clone(FlagOpFn op, const void* obj) {
return op(flags_internal::kClone, obj, nullptr);
}
inline void Copy(FlagOpFn op, const void* src, void* dst) {
op(flags_internal::kCopy, src, dst);
}
inline void CopyConstruct(FlagOpFn op, const void* src, void* dst) {
op(flags_internal::kCopyConstruct, src, dst);
}
inline bool Parse(FlagMarshallingOpFn op, absl::string_view text, void* dst,
std::string* error) {
return op(flags_internal::kParse, &text, dst, error) != nullptr;
}
inline std::string Unparse(FlagMarshallingOpFn op, const void* val) {
std::string result;
op(flags_internal::kUnparse, val, &result, nullptr);
return result;
}
inline size_t Sizeof(FlagOpFn op) {
// This sequence of casts reverses the sequence from base::internal::FlagOps()
return static_cast<size_t>(reinterpret_cast<intptr_t>(
op(flags_internal::kSizeof, nullptr, nullptr)));
}
// 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;
// Virtual destructor
virtual void Destroy() = 0;
// 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::FlagOps<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 flags_internal::FlagOpFn 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_