Alex Vakulenko | e4eec20 | 2017-01-27 14:41:04 -0800 | [diff] [blame^] | 1 | #ifndef ANDROID_PDX_STATUS_H_ |
| 2 | #define ANDROID_PDX_STATUS_H_ |
| 3 | |
| 4 | #include <algorithm> |
| 5 | #include <memory> |
| 6 | #include <string> |
| 7 | |
| 8 | namespace android { |
| 9 | namespace pdx { |
| 10 | |
| 11 | // This is a helper class for constructing Status<T> with an error code. |
| 12 | struct ErrorStatus { |
| 13 | public: |
| 14 | ErrorStatus(int error) : error_{error} {} |
| 15 | int error() const { return error_; } |
| 16 | |
| 17 | static std::string ErrorToString(int error_code); |
| 18 | |
| 19 | private: |
| 20 | int error_; |
| 21 | }; |
| 22 | |
| 23 | // Status<T> is a container class that can be used to return a value of type T |
| 24 | // or error code to the caller. |
| 25 | template <typename T> |
| 26 | class Status { |
| 27 | public: |
| 28 | // Default constructor so an empty Status object can be created. |
| 29 | Status() : error_{-1} {} |
| 30 | |
| 31 | // Value copy/move constructors. These are intentionally not marked as |
| 32 | // explicit to allow direct value returns from functions without having |
| 33 | // to explicitly wrap them into Status<T>(). |
| 34 | Status(const T& value) : value_{value} {} // NOLINT(runtime/explicit) |
| 35 | Status(T&& value) : value_{std::move(value)} {} // NOLINT(runtime/explicit) |
| 36 | |
| 37 | // Constructor for storing an error code inside the Status object. |
| 38 | Status(const ErrorStatus& error_status) // NOLINT(runtime/explicit) |
| 39 | : error_{error_status.error()} {} |
| 40 | |
| 41 | // Copy/move constructors. Move constructor leaves |other| object in empty |
| 42 | // state. |
| 43 | Status(const Status& other) = default; |
| 44 | Status(Status&& other) |
| 45 | : value_{std::move(other.value_)}, error_{other.error_} { |
| 46 | other.error_ = -1; |
| 47 | } |
| 48 | |
| 49 | // Assignment operators. |
| 50 | Status& operator=(const Status& other) = default; |
| 51 | Status& operator=(Status&& other) { |
| 52 | error_ = other.error_; |
| 53 | value_ = std::move(other.value_); |
| 54 | other.error_ = -1; |
| 55 | T empty; |
| 56 | std::swap(other.value_, empty); |
| 57 | return *this; |
| 58 | } |
| 59 | |
| 60 | // Change the value/error code of the status object directly. |
| 61 | void SetValue(T value) { |
| 62 | error_ = 0; |
| 63 | value_ = std::move(value); |
| 64 | } |
| 65 | void SetError(int error) { |
| 66 | error_ = error; |
| 67 | T empty; |
| 68 | std::swap(value_, empty); |
| 69 | } |
| 70 | |
| 71 | // If |other| is in error state, copy the error code to this object. |
| 72 | // Returns true if error was propagated |
| 73 | template<typename U> |
| 74 | bool PropagateError(const Status<U>& other) { |
| 75 | if (!other.ok() && !other.empty()) { |
| 76 | SetError(other.error()); |
| 77 | return true; |
| 78 | } |
| 79 | return false; |
| 80 | } |
| 81 | |
| 82 | // Returns true if the status object contains valid value for type T. |
| 83 | // This means, the object is not empty and does not contain an error code. |
| 84 | bool ok() const { return error_ == 0; } |
| 85 | |
| 86 | // Checks if the object is empty (doesn't contain a valid value nor an error). |
| 87 | bool empty() const { return error_ < 0; } |
| 88 | |
| 89 | // Explicit bool conversion, equivalent to invoking ok(). |
| 90 | explicit operator bool() const { return ok(); } |
| 91 | |
| 92 | // Accessors for the value stored in Status. Calling when ok() is false leads |
| 93 | // to undefined behavior. |
| 94 | const T& get() const { return value_; } |
| 95 | T&& take() { |
| 96 | error_ = -1; |
| 97 | return std::move(value_); |
| 98 | } |
| 99 | |
| 100 | // Returns the error code stored in the object. These codes are positive |
| 101 | // non-zero values. |
| 102 | // Can be called only when an error is actually stored (that is, the object |
| 103 | // is not empty nor containing a valid value). |
| 104 | int error() const { return std::max(error_, 0); } |
| 105 | |
| 106 | // Returns the error message associated with error code stored in the object. |
| 107 | // The message is the same as the string returned by strerror(status.error()). |
| 108 | // Can be called only when an error is actually stored (that is, the object |
| 109 | // is not empty nor containing a valid value). |
| 110 | std::string GetErrorMessage() const { |
| 111 | std::string message; |
| 112 | if (error_ > 0) |
| 113 | message = ErrorStatus::ErrorToString(error_); |
| 114 | return message; |
| 115 | } |
| 116 | |
| 117 | private: |
| 118 | T value_{}; |
| 119 | int error_{0}; |
| 120 | }; |
| 121 | |
| 122 | // Specialization for status containing no other value but the error code. |
| 123 | template <> |
| 124 | class Status<void> { |
| 125 | public: |
| 126 | Status() = default; |
| 127 | Status(const ErrorStatus& error_status) // NOLINT(runtime/explicit) |
| 128 | : error_{error_status.error()} {} |
| 129 | void SetValue() { error_ = 0; } |
| 130 | void SetError(int error) { error_ = error; } |
| 131 | |
| 132 | template<typename U> |
| 133 | bool PropagateError(const Status<U>& other) { |
| 134 | if (!other.ok() && !other.empty()) { |
| 135 | SetError(other.error()); |
| 136 | return true; |
| 137 | } |
| 138 | return false; |
| 139 | } |
| 140 | |
| 141 | bool ok() const { return error_ == 0; } |
| 142 | bool empty() const { return false; } |
| 143 | explicit operator bool() const { return ok(); } |
| 144 | int error() const { return std::max(error_, 0); } |
| 145 | std::string GetErrorMessage() const { |
| 146 | std::string message; |
| 147 | if (error_ > 0) |
| 148 | message = ErrorStatus::ErrorToString(error_); |
| 149 | return message; |
| 150 | } |
| 151 | |
| 152 | private: |
| 153 | int error_{0}; |
| 154 | }; |
| 155 | |
| 156 | // TODO(avakulenko): Remove these function once all callers of it are gone. |
| 157 | inline int ReturnStatusOrError(const Status<void>& status) { |
| 158 | return status ? 0 : -status.error(); |
| 159 | } |
| 160 | |
| 161 | inline int ReturnStatusOrError(const Status<int>& status) { |
| 162 | return status ? status.get() : -status.error(); |
| 163 | } |
| 164 | |
| 165 | } // namespace pdx |
| 166 | } // namespace android |
| 167 | |
| 168 | #endif // ANDROID_PDX_STATUS_H_ |