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Export of internal Abseil changes.

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--
ed3a3431eee9e48e6553b0320e0308d2dde6725c by Derek Mauro <dmauro@google.com>:

Project import generated by Copybara.

PiperOrigin-RevId: 258631680
GitOrigin-RevId: ed3a3431eee9e48e6553b0320e0308d2dde6725c
Change-Id: I1d7ae86a79783842092d29504605ba039c369603
This commit is contained in:
Abseil Team 2019-07-17 16:35:47 -04:00 • committed by Derek Mauro
parent 44efe96dfc
commit c6c3c1b498
32 changed files with 1168 additions and 657 deletions
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72
absl/flags/internal/flag.h
View file

@ -24,40 +24,58 @@ namespace flags_internal {
// This is "unspecified" implementation of absl::Flag<T> type.
template <typename T>
class Flag {
class Flag : public flags_internal::CommandLineFlag {
public:
constexpr Flag(const char* name, const flags_internal::HelpGenFunc help_gen,
const char* filename,
const flags_internal::FlagMarshallingOpFn marshalling_op,
const flags_internal::FlagMarshallingOpFn marshalling_op_arg,
const flags_internal::InitialValGenFunc initial_value_gen)
: internal(name, flags_internal::HelpText::FromFunctionPointer(help_gen),
filename, &flags_internal::FlagOps<T>, marshalling_op,
initial_value_gen,
/*retired_arg=*/false, /*def_arg=*/nullptr,
/*cur_arg=*/nullptr) {}
: flags_internal::CommandLineFlag(
name, flags_internal::HelpText::FromFunctionPointer(help_gen),
filename, &flags_internal::FlagOps<T>, marshalling_op_arg,
initial_value_gen,
/*retired_arg=*/false, /*def_arg=*/nullptr,
/*cur_arg=*/nullptr) {}
// Not copyable/assignable.
Flag(const Flag<T>&) = delete;
Flag<T>& operator=(const Flag<T>&) = delete;
T Get() const {
// 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;
absl::string_view Name() const { return internal.Name(); }
std::string Help() const { return internal.Help(); }
std::string Filename() const { return internal.Filename(); }
absl::flags_internal::CommandLineFlag internal;
void SetCallback(const flags_internal::FlagCallback mutation_callback) {
internal.SetCallback(mutation_callback);
this->Read(&u.value, &flags_internal::FlagOps<T>);
return std::move(u.value);
}
private:
// TODO(rogeeff): add these validations once UnparseFlag invocation is fixed
// for built-in types and when we cleanup existing code from operating on
// forward declared types.
// auto IsCopyConstructible(const T& v) -> decltype(T(v));
// auto HasAbslParseFlag(absl::string_view in, T* dst, std::string* err)
// -> decltype(AbslParseFlag(in, dst, err));
// auto HasAbslUnparseFlag(const T& v) -> decltype(AbslUnparseFlag(v));
bool AtomicGet(T* v) const {
const int64_t r = this->atomic.load(std::memory_order_acquire);
if (r != flags_internal::CommandLineFlag::kAtomicInit) {
memcpy(v, &r, sizeof(T));
return true;
}
return false;
}
void Set(const T& v) { this->Write(&v, &flags_internal::FlagOps<T>); }
};
// This class facilitates Flag object registration and tail expression-based
@ -67,7 +85,7 @@ template <typename T, bool do_register>
class FlagRegistrar {
public:
explicit FlagRegistrar(Flag<T>* flag) : flag_(flag) {
if (do_register) flags_internal::RegisterCommandLineFlag(&flag_->internal);
if (do_register) flags_internal::RegisterCommandLineFlag(flag_);
}
FlagRegistrar& OnUpdate(flags_internal::FlagCallback cb) && {