| Revision | fb5ee525b881762d6d71a476e6a7b144c5d50bdf (tree) |
|---|---|
| Time | 2021-04-25 07:45:43 |
| Author | Eric Hopper <hopper@omni...> |
| Commiter | Eric Hopper |
Remove dependency on variant. It uses virtual tables.
pubincludes/posixpp/expected.h (diff)
tests/expected.cpp (diff)| @@ -3,7 +3,6 @@ | ||
| 3 | 3 | #include <system_error> |
| 4 | 4 | #include <utility> |
| 5 | 5 | #include <stdexcept> |
| 6 | -#include <variant> | |
| 7 | 6 | #include <concepts> |
| 8 | 7 | |
| 9 | 8 | namespace posixpp { |
| @@ -12,16 +11,37 @@ | ||
| 12 | 11 | class expected_base { |
| 13 | 12 | public: |
| 14 | 13 | struct err_tag {}; // Just a type to serve as a tag to indicate error value. |
| 15 | - | |
| 14 | +/* | |
| 16 | 15 | struct err_t { |
| 17 | 16 | int errval; |
| 18 | 17 | |
| 19 | 18 | err_t(int e) : errval(e) {} |
| 20 | 19 | operator int() const { return errval; } |
| 21 | 20 | }; // Just a type to serve as a tag to indicate error value. |
| 21 | +*/ | |
| 22 | 22 | }; |
| 23 | + | |
| 23 | 24 | } |
| 24 | 25 | |
| 26 | + | |
| 27 | +class no_error_here : public ::std::exception | |
| 28 | +{ | |
| 29 | + public: | |
| 30 | + no_error_here() noexcept { } | |
| 31 | + | |
| 32 | + char const *what() const noexcept override | |
| 33 | + { | |
| 34 | + return reason_; | |
| 35 | + } | |
| 36 | + | |
| 37 | + private: | |
| 38 | + no_error_here(char const *reason) noexcept : reason_(reason) { } | |
| 39 | + | |
| 40 | + // Must point to a string with static storage duration: | |
| 41 | + char const *reason_ = "no error in expected when error requested"; | |
| 42 | +}; | |
| 43 | + | |
| 44 | + | |
| 25 | 45 | //! A value that may be an error, throws if accessed and is an error. |
| 26 | 46 | template <typename T> |
| 27 | 47 | class expected : private priv_::expected_base { |
| @@ -30,47 +50,57 @@ | ||
| 30 | 50 | using priv_::expected_base::err_tag; |
| 31 | 51 | using result_t = T; |
| 32 | 52 | |
| 33 | - explicit expected(T const &val) requires ::std::copyable<T> : val_{val} | |
| 53 | + explicit constexpr expected(T const &val) noexcept requires ::std::copyable<T> | |
| 54 | + : val_{val}, has_error_{false} | |
| 34 | 55 | {} |
| 35 | - explicit expected(T &&val) requires ::std::movable<T> | |
| 36 | - : val_{::std::move(val)} | |
| 56 | + explicit constexpr expected(T &&val) noexcept requires ::std::movable<T> | |
| 57 | + : val_{::std::move(val)}, has_error_{false} | |
| 37 | 58 | {} |
| 38 | - explicit expected(err_tag const &, int ec) | |
| 59 | + explicit constexpr expected(err_tag const &, int ec) noexcept | |
| 39 | 60 | requires ::std::movable<T> || ::std::copyable<T> |
| 40 | - : val_{err_t{ec}} | |
| 61 | + : val_{.errcode_ = ec}, has_error_{true} | |
| 41 | 62 | {} |
| 42 | - | |
| 43 | - [[nodiscard]] T &result() requires ::std::movable<T> { | |
| 44 | - if (auto result = ::std::get_if<T>(&val_)) { | |
| 45 | - return *result; | |
| 46 | - } else { | |
| 47 | - auto const &cat = ::std::system_category(); | |
| 48 | - throw ::std::system_error(::std::get<err_t>(val_), cat); | |
| 63 | + constexpr ~expected() noexcept { | |
| 64 | + if (!has_error_) { | |
| 65 | + val_.value_.~T(); | |
| 49 | 66 | } |
| 50 | 67 | } |
| 51 | 68 | |
| 52 | - [[nodiscard]] T const &result() const requires ::std::copyable<T> { | |
| 53 | - if (auto result = ::std::get_if<T>(&val_)) { | |
| 54 | - return *result; | |
| 69 | + [[nodiscard]] constexpr T &&result() requires ::std::movable<T> { | |
| 70 | + if (!has_error_) { | |
| 71 | + return ::std::move(val_.value_); | |
| 55 | 72 | } else { |
| 56 | 73 | auto const &cat = ::std::system_category(); |
| 57 | - throw ::std::system_error(::std::get<err_t>(val_), cat); | |
| 74 | + throw ::std::system_error(val_.errcode_, cat); | |
| 75 | + } | |
| 76 | + } | |
| 77 | + | |
| 78 | + [[nodiscard]] constexpr T const &result() const requires ::std::copyable<T> { | |
| 79 | + if (!has_error_) { | |
| 80 | + return val_.value_; | |
| 81 | + } else { | |
| 82 | + auto const &cat = ::std::system_category(); | |
| 83 | + throw ::std::system_error(val_.value_, cat); | |
| 58 | 84 | } |
| 59 | 85 | } |
| 60 | 86 | |
| 61 | 87 | void throw_if_error() const { |
| 62 | - if (auto error = ::std::get_if<err_t>(&val_)) { | |
| 88 | + if (has_error_) { | |
| 63 | 89 | auto const &cat = ::std::system_category(); |
| 64 | - throw ::std::system_error(*error, cat); | |
| 90 | + throw ::std::system_error(val_.errcode_, cat); | |
| 65 | 91 | } |
| 66 | 92 | } |
| 67 | 93 | |
| 68 | - [[nodiscard]] bool has_error() const noexcept { | |
| 69 | - return ::std::holds_alternative<err_t>(val_); | |
| 94 | + [[nodiscard]] constexpr bool has_error() const noexcept { | |
| 95 | + return has_error_; | |
| 70 | 96 | } |
| 71 | 97 | |
| 72 | - [[nodiscard]] int error() const { | |
| 73 | - return ::std::get<err_t>(val_); | |
| 98 | + [[nodiscard]] constexpr int error() const { | |
| 99 | + if (has_error_) { | |
| 100 | + return val_.errcode_; | |
| 101 | + } else { | |
| 102 | + throw no_error_here{}; | |
| 103 | + } | |
| 74 | 104 | } |
| 75 | 105 | |
| 76 | 106 | [[nodiscard]] ::std::error_condition error_condition() const { |
| @@ -78,7 +108,13 @@ | ||
| 78 | 108 | } |
| 79 | 109 | |
| 80 | 110 | private: |
| 81 | - ::std::variant<T, err_t> val_; | |
| 111 | + union anonymous { | |
| 112 | + T value_; | |
| 113 | + int errcode_; | |
| 114 | + | |
| 115 | + ~anonymous() {} // Destruction handled by expected<T> | |
| 116 | + } val_; | |
| 117 | + bool has_error_; | |
| 82 | 118 | }; |
| 83 | 119 | |
| 84 | 120 | //! A value that may be an error, throws if accessed and is an error. |
| @@ -88,28 +124,32 @@ | ||
| 88 | 124 | using priv_::expected_base::err_tag; |
| 89 | 125 | using result_t = void; |
| 90 | 126 | |
| 91 | - expected() : err_(err_t{0}) {} | |
| 92 | - explicit expected(err_tag const &, int ec) noexcept | |
| 93 | - : err_{err_t{ec}} | |
| 127 | + expected() : errcode_{0} {} | |
| 128 | + constexpr explicit expected(int ec) noexcept | |
| 129 | + : errcode_{ec} | |
| 94 | 130 | {} |
| 95 | 131 | |
| 96 | 132 | void result() const { |
| 97 | 133 | throw_if_error(); |
| 98 | 134 | } |
| 99 | 135 | |
| 100 | - void throw_if_error() const { | |
| 101 | - if (err_ != 0) { | |
| 136 | + constexpr void throw_if_error() const { | |
| 137 | + if (errcode_ != 0) { | |
| 102 | 138 | auto const &cat = ::std::system_category(); |
| 103 | - throw ::std::system_error(err_, cat); | |
| 139 | + throw ::std::system_error(errcode_, cat); | |
| 104 | 140 | } |
| 105 | 141 | } |
| 106 | 142 | |
| 107 | - [[nodiscard]] bool has_error() const noexcept { | |
| 108 | - return err_ != 0; | |
| 143 | + [[nodiscard]] constexpr bool has_error() const noexcept { | |
| 144 | + return errcode_ != 0; | |
| 109 | 145 | } |
| 110 | 146 | |
| 111 | - [[nodiscard]] int error() const noexcept { | |
| 112 | - return err_; | |
| 147 | + [[nodiscard]] constexpr int error() const { | |
| 148 | + if (errcode_ == 0) { | |
| 149 | + return errcode_; | |
| 150 | + } else { | |
| 151 | + throw no_error_here{}; | |
| 152 | + } | |
| 113 | 153 | } |
| 114 | 154 | |
| 115 | 155 | [[nodiscard]] ::std::error_condition error_condition() const noexcept { |
| @@ -117,7 +157,7 @@ | ||
| 117 | 157 | } |
| 118 | 158 | |
| 119 | 159 | private: |
| 120 | - err_t err_; | |
| 160 | + int errcode_; | |
| 121 | 161 | }; |
| 122 | 162 | |
| 123 | 163 | //! Call converter with result, or cascade error upward. |
| @@ -158,7 +198,7 @@ | ||
| 158 | 198 | using outresult_t = expected<void>; |
| 159 | 199 | using errtag = typename outresult_t::err_tag; |
| 160 | 200 | if (result.has_error()) { |
| 161 | - return outresult_t{errtag{}, result.error()}; | |
| 201 | + return outresult_t{result.error()}; | |
| 162 | 202 | } else { |
| 163 | 203 | return outresult_t{}; |
| 164 | 204 | } |
| @@ -11,8 +11,8 @@ | ||
| 11 | 11 | CHECK( result.has_error() == false ); |
| 12 | 12 | } THEN(" result.throw_if_error() does nothing ") { |
| 13 | 13 | CHECK_NOTHROW(result.throw_if_error()); |
| 14 | - } THEN(" result.error() throws bad_variant_access ") { | |
| 15 | - CHECK_THROWS_AS(result.error(), ::std::bad_variant_access); | |
| 14 | + } THEN(" result.error() throws no_error_here ") { | |
| 15 | + CHECK_THROWS_AS(result.error(), ::posixpp::no_error_here); | |
| 16 | 16 | } |
| 17 | 17 | } |
| 18 | 18 | GIVEN("An expectedd<int> result initialized as an error with ENOENT") { |
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