llvm-6502/include/llvm/Support/ErrorOr.h
Michael J. Spencer 780e9004c8 [Support][ErrorOr] Add support for convertable types.
Thanks to Andrew, David, and Aaron for helping fix this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174552 91177308-0d34-0410-b5e6-96231b3b80d8
2013-02-06 22:28:53 +00:00

489 lines
12 KiB
C++

//===- llvm/Support/ErrorOr.h - Error Smart Pointer -----------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
///
/// Provides ErrorOr<T> smart pointer.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_SUPPORT_ERROR_OR_H
#define LLVM_SUPPORT_ERROR_OR_H
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/Support/AlignOf.h"
#include "llvm/Support/system_error.h"
#include "llvm/Support/type_traits.h"
#include <cassert>
#if LLVM_HAS_CXX11_TYPETRAITS
#include <type_traits>
#endif
namespace llvm {
struct ErrorHolderBase {
error_code Error;
uint16_t RefCount;
bool HasUserData;
ErrorHolderBase() : RefCount(1) {}
void aquire() {
++RefCount;
}
void release() {
if (--RefCount == 0)
delete this;
}
protected:
virtual ~ErrorHolderBase() {}
};
template<class T>
struct ErrorHolder : ErrorHolderBase {
#if LLVM_HAS_RVALUE_REFERENCES
ErrorHolder(T &&UD) : UserData(llvm_move(UD)) {}
#else
ErrorHolder(T &UD) : UserData(UD) {}
#endif
T UserData;
};
template<class Tp> struct ErrorOrUserDataTraits : llvm::false_type {};
#if LLVM_HAS_CXX11_TYPETRAITS && LLVM_HAS_RVALUE_REFERENCES
template<class T, class V>
typename std::enable_if< std::is_constructible<T, V>::value
, typename std::remove_reference<V>::type>::type &&
moveIfMoveConstructible(V &Val) {
return std::move(Val);
}
template<class T, class V>
typename std::enable_if< !std::is_constructible<T, V>::value
, typename std::remove_reference<V>::type>::type &
moveIfMoveConstructible(V &Val) {
return Val;
}
#else
template<class T, class V>
V &moveIfMoveConstructible(V &Val) {
return Val;
}
#endif
/// \brief Stores a reference that can be changed.
template <typename T>
class ReferenceStorage {
T *Storage;
public:
ReferenceStorage(T &Ref) : Storage(&Ref) {}
operator T &() const { return *Storage; }
T &get() const { return *Storage; }
};
/// \brief Represents either an error or a value T.
///
/// ErrorOr<T> is a pointer-like class that represents the result of an
/// operation. The result is either an error, or a value of type T. This is
/// designed to emulate the usage of returning a pointer where nullptr indicates
/// failure. However instead of just knowing that the operation failed, we also
/// have an error_code and optional user data that describes why it failed.
///
/// It is used like the following.
/// \code
/// ErrorOr<Buffer> getBuffer();
/// void handleError(error_code ec);
///
/// auto buffer = getBuffer();
/// if (!buffer)
/// handleError(buffer);
/// buffer->write("adena");
/// \endcode
///
/// ErrorOr<T> also supports user defined data for specific error_codes. To use
/// this feature you must first add a template specialization of
/// ErrorOrUserDataTraits derived from std::true_type for your type in the lld
/// namespace. This specialization must have a static error_code error()
/// function that returns the error_code this data is used with.
///
/// getError<UserData>() may be called to get either the stored user data, or
/// a default constructed UserData if none was stored.
///
/// Example:
/// \code
/// struct InvalidArgError {
/// InvalidArgError() {}
/// InvalidArgError(std::string S) : ArgName(S) {}
/// std::string ArgName;
/// };
///
/// namespace llvm {
/// template<>
/// struct ErrorOrUserDataTraits<InvalidArgError> : std::true_type {
/// static error_code error() {
/// return make_error_code(errc::invalid_argument);
/// }
/// };
/// } // end namespace llvm
///
/// using namespace llvm;
///
/// ErrorOr<int> foo() {
/// return InvalidArgError("adena");
/// }
///
/// int main() {
/// auto a = foo();
/// if (!a && error_code(a) == errc::invalid_argument)
/// llvm::errs() << a.getError<InvalidArgError>().ArgName << "\n";
/// }
/// \endcode
///
/// An implicit conversion to bool provides a way to check if there was an
/// error. The unary * and -> operators provide pointer like access to the
/// value. Accessing the value when there is an error has undefined behavior.
///
/// When T is a reference type the behaivor is slightly different. The reference
/// is held in a std::reference_wrapper<std::remove_reference<T>::type>, and
/// there is special handling to make operator -> work as if T was not a
/// reference.
///
/// T cannot be a rvalue reference.
template<class T>
class ErrorOr {
template <class OtherT> friend class ErrorOr;
static const bool isRef = is_reference<T>::value;
typedef ReferenceStorage<typename remove_reference<T>::type> wrap;
public:
typedef typename
conditional< isRef
, wrap
, T
>::type storage_type;
private:
typedef typename remove_reference<T>::type &reference;
typedef typename remove_reference<T>::type *pointer;
public:
ErrorOr() : IsValid(false) {}
ErrorOr(llvm::error_code EC) : HasError(true), IsValid(true) {
Error = new ErrorHolderBase;
Error->Error = EC;
Error->HasUserData = false;
}
template<class UserDataT>
ErrorOr(UserDataT UD, typename
enable_if_c<ErrorOrUserDataTraits<UserDataT>::value>::type* = 0)
: HasError(true), IsValid(true) {
Error = new ErrorHolder<UserDataT>(llvm_move(UD));
Error->Error = ErrorOrUserDataTraits<UserDataT>::error();
Error->HasUserData = true;
}
ErrorOr(T Val) : HasError(false), IsValid(true) {
new (get()) storage_type(moveIfMoveConstructible<storage_type>(Val));
}
ErrorOr(const ErrorOr &Other) : IsValid(false) {
copyConstruct(Other);
}
template <class OtherT>
ErrorOr(const ErrorOr<OtherT> &Other) : IsValid(false) {
copyConstruct(Other);
}
ErrorOr &operator =(const ErrorOr &Other) {
copyAssign(Other);
return *this;
}
template <class OtherT>
ErrorOr &operator =(const ErrorOr<OtherT> &Other) {
copyAssign(Other);
return *this;
}
#if LLVM_HAS_RVALUE_REFERENCES
ErrorOr(ErrorOr &&Other) : IsValid(false) {
moveConstruct(std::move(Other));
}
template <class OtherT>
ErrorOr(ErrorOr<OtherT> &&Other) : IsValid(false) {
moveConstruct(std::move(Other));
}
ErrorOr &operator =(ErrorOr &&Other) {
moveAssign(std::move(Other));
return *this;
}
template <class OtherT>
ErrorOr &operator =(ErrorOr<OtherT> &&Other) {
moveAssign(std::move(Other));
return *this;
}
#endif
~ErrorOr() {
if (!IsValid)
return;
if (HasError)
Error->release();
else
get()->~storage_type();
}
template<class ET>
ET getError() const {
assert(IsValid && "Cannot get the error of a default constructed ErrorOr!");
assert(HasError && "Cannot get an error if none exists!");
assert(ErrorOrUserDataTraits<ET>::error() == Error->Error &&
"Incorrect user error data type for error!");
if (!Error->HasUserData)
return ET();
return reinterpret_cast<const ErrorHolder<ET>*>(Error)->UserData;
}
typedef void (*unspecified_bool_type)();
static void unspecified_bool_true() {}
/// \brief Return false if there is an error.
operator unspecified_bool_type() const {
assert(IsValid && "Can't do anything on a default constructed ErrorOr!");
return HasError ? 0 : unspecified_bool_true;
}
operator llvm::error_code() const {
assert(IsValid && "Can't do anything on a default constructed ErrorOr!");
return HasError ? Error->Error : llvm::error_code::success();
}
pointer operator ->() {
return toPointer(get());
}
reference operator *() {
return *get();
}
private:
template <class OtherT>
void copyConstruct(const ErrorOr<OtherT> &Other) {
// Construct an invalid ErrorOr if other is invalid.
if (!Other.IsValid)
return;
IsValid = true;
if (!Other.HasError) {
// Get the other value.
HasError = false;
new (get()) storage_type(*Other.get());
} else {
// Get other's error.
Error = Other.Error;
HasError = true;
Error->aquire();
}
}
template <class T1>
static bool compareThisIfSameType(const T1 &a, const T1 &b) {
return &a == &b;
}
template <class T1, class T2>
static bool compareThisIfSameType(const T1 &a, const T2 &b) {
return false;
}
template <class OtherT>
void copyAssign(const ErrorOr<OtherT> &Other) {
if (compareThisIfSameType(*this, Other))
return;
this->~ErrorOr();
new (this) ErrorOr(Other);
}
#if LLVM_HAS_RVALUE_REFERENCES
template <class OtherT>
void moveConstruct(ErrorOr<OtherT> &&Other) {
// Construct an invalid ErrorOr if other is invalid.
if (!Other.IsValid)
return;
IsValid = true;
if (!Other.HasError) {
// Get the other value.
HasError = false;
new (get()) storage_type(std::move(*Other.get()));
// Tell other not to do any destruction.
Other.IsValid = false;
} else {
// Get other's error.
Error = Other.Error;
HasError = true;
// Tell other not to do any destruction.
Other.IsValid = false;
}
}
template <class OtherT>
void moveAssign(ErrorOr<OtherT> &&Other) {
if (compareThisIfSameType(*this, Other))
return;
this->~ErrorOr();
new (this) ErrorOr(std::move(Other));
}
#endif
pointer toPointer(pointer Val) {
return Val;
}
pointer toPointer(wrap *Val) {
return &Val->get();
}
storage_type *get() {
assert(IsValid && "Can't do anything on a default constructed ErrorOr!");
assert(!HasError && "Cannot get value when an error exists!");
return reinterpret_cast<storage_type*>(TStorage.buffer);
}
const storage_type *get() const {
assert(IsValid && "Can't do anything on a default constructed ErrorOr!");
assert(!HasError && "Cannot get value when an error exists!");
return reinterpret_cast<const storage_type*>(TStorage.buffer);
}
union {
AlignedCharArrayUnion<storage_type> TStorage;
ErrorHolderBase *Error;
};
bool HasError : 1;
bool IsValid : 1;
};
// ErrorOr specialization for void.
template <>
class ErrorOr<void> {
public:
ErrorOr() : Error(0, 0) {}
ErrorOr(llvm::error_code EC) : Error(0, 0) {
if (EC == errc::success) {
Error.setInt(1);
return;
}
ErrorHolderBase *E = new ErrorHolderBase;
E->Error = EC;
E->HasUserData = false;
Error.setPointer(E);
}
template<class UserDataT>
ErrorOr(UserDataT UD, typename
enable_if_c<ErrorOrUserDataTraits<UserDataT>::value>::type* = 0)
: Error(0, 0) {
ErrorHolderBase *E = new ErrorHolder<UserDataT>(llvm_move(UD));
E->Error = ErrorOrUserDataTraits<UserDataT>::error();
E->HasUserData = true;
Error.setPointer(E);
}
ErrorOr(const ErrorOr &Other) : Error(0, 0) {
Error = Other.Error;
if (Other.Error.getPointer()->Error) {
Error.getPointer()->aquire();
}
}
ErrorOr &operator =(const ErrorOr &Other) {
if (this == &Other)
return *this;
this->~ErrorOr();
new (this) ErrorOr(Other);
return *this;
}
#if LLVM_HAS_RVALUE_REFERENCES
ErrorOr(ErrorOr &&Other) : Error(0) {
// Get other's error.
Error = Other.Error;
// Tell other not to do any destruction.
Other.Error.setPointer(0);
}
ErrorOr &operator =(ErrorOr &&Other) {
if (this == &Other)
return *this;
this->~ErrorOr();
new (this) ErrorOr(std::move(Other));
return *this;
}
#endif
~ErrorOr() {
if (Error.getPointer())
Error.getPointer()->release();
}
template<class ET>
ET getError() const {
assert(ErrorOrUserDataTraits<ET>::error() == *this &&
"Incorrect user error data type for error!");
if (!Error.getPointer()->HasUserData)
return ET();
return reinterpret_cast<const ErrorHolder<ET> *>(
Error.getPointer())->UserData;
}
typedef void (*unspecified_bool_type)();
static void unspecified_bool_true() {}
/// \brief Return false if there is an error.
operator unspecified_bool_type() const {
return Error.getInt() ? unspecified_bool_true : 0;
}
operator llvm::error_code() const {
return Error.getInt() ? make_error_code(errc::success)
: Error.getPointer()->Error;
}
private:
// If the bit is 1, the error is success.
llvm::PointerIntPair<ErrorHolderBase *, 1> Error;
};
template<class T, class E>
typename enable_if_c<is_error_code_enum<E>::value ||
is_error_condition_enum<E>::value, bool>::type
operator ==(ErrorOr<T> &Err, E Code) {
return error_code(Err) == Code;
}
} // end namespace llvm
#endif