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| 1 /* |
| 2 * Copyright 2016 Google Inc. |
| 3 * |
| 4 * Use of this source code is governed by a BSD-style license that can be |
| 5 * found in the LICENSE file. |
| 6 */ |
| 7 |
| 8 #ifndef SkPEG_DEFINED |
| 9 #define SkPEG_DEFINED |
| 10 |
| 11 #include "SkTArray.h" |
| 12 #include "SkTLazy.h" |
| 13 |
| 14 namespace skpeg { |
| 15 |
| 16 /** |
| 17 * The result of an expression match attempt. |
| 18 * |
| 19 * If the match was successful, |fNext| points to the next unconsumed character
in the |
| 20 * input string, and |fValue| holds an (arbitrarily nested) match result value. |
| 21 * |
| 22 * Otherwise, |fNext| is nullptr and |fValue| is uninitialized. |
| 23 */ |
| 24 template <typename V> |
| 25 struct MatchResult { |
| 26 MatchResult(std::nullptr_t) : fNext(nullptr) {} |
| 27 MatchResult(const char* next, const V& v) : fNext(next), fValue(&v) {} |
| 28 |
| 29 operator bool() const { |
| 30 SkASSERT(fValue.isValid() == SkToBool(fNext)); |
| 31 return SkToBool(fNext); |
| 32 } |
| 33 |
| 34 const V& operator* () const { return *fValue.get(); } |
| 35 const V* operator->() const { return fValue.get(); } |
| 36 |
| 37 const char* fNext; |
| 38 SkTLazy<V> fValue; |
| 39 }; |
| 40 |
| 41 /** |
| 42 * Optional operator (e?). Always succeeds. |
| 43 * |
| 44 * If e also matches, then the result of e::Match() is stored in |fValue|. |
| 45 * Otherwise, |fValue| is uninitialized. |
| 46 * |
| 47 */ |
| 48 template <typename E> |
| 49 struct Opt { |
| 50 struct V { |
| 51 V(const typename E::V* v) : fValue(v) {} |
| 52 |
| 53 SkTLazy<typename E::V> fValue; |
| 54 }; |
| 55 using MatchT = MatchResult<V>; |
| 56 |
| 57 static MatchT Match(const char* in) { |
| 58 const auto m = E::Match(in); |
| 59 return m ? MatchT(m.fNext, V(m.fValue.get())) |
| 60 : MatchT(in, nullptr); |
| 61 } |
| 62 }; |
| 63 |
| 64 /** |
| 65 * Helper for selecting the value type of the n-th expression type in the list. |
| 66 */ |
| 67 template <size_t, typename... Es> struct SelectV; |
| 68 |
| 69 template <typename E, typename... Es> |
| 70 struct SelectV<0, E, Es...> { |
| 71 using V = typename E::V; |
| 72 }; |
| 73 |
| 74 template <size_t idx, typename E, typename... Es> |
| 75 struct SelectV<idx, E, Es...> { |
| 76 using V = typename SelectV<idx - 1, Es...>::V; |
| 77 }; |
| 78 |
| 79 /** |
| 80 * Sequence operator (e0 e1...). |
| 81 * |
| 82 * Succeeds when all expressions match, in sequence. The subexpression match |
| 83 * results can be accessed via get<INDEX>() -- where get<0> returns the value |
| 84 * of the first expression, and so on. |
| 85 * |
| 86 */ |
| 87 template <typename... E> struct Seq; |
| 88 |
| 89 template <> |
| 90 struct Seq<> { |
| 91 struct V {}; |
| 92 using MatchT = MatchResult<V>; |
| 93 |
| 94 static MatchT Match(const char* in) { |
| 95 return MatchT(in, V()); |
| 96 } |
| 97 }; |
| 98 |
| 99 template <typename E, typename... Es> |
| 100 struct Seq<E, Es...> { |
| 101 class V { |
| 102 public: |
| 103 V(const typename E::V& head, const typename Seq<Es...>::V& tail) |
| 104 : fHeadV(head), fTailV(tail) {} |
| 105 |
| 106 template <size_t idx, typename std::enable_if<idx == 0, bool>::type = 0> |
| 107 const typename E::V& get() const { |
| 108 return fHeadV; |
| 109 } |
| 110 |
| 111 template <size_t idx, typename std::enable_if<idx != 0, bool>::type = 0> |
| 112 const typename SelectV<idx, E, Es...>::V& get() const { |
| 113 return fTailV.template get<idx - 1>(); |
| 114 } |
| 115 |
| 116 private: |
| 117 typename E::V fHeadV; |
| 118 typename Seq<Es...>::V fTailV; |
| 119 }; |
| 120 using MatchT = MatchResult<V>; |
| 121 |
| 122 static MatchT Match(const char* in) { |
| 123 const auto headMatch = E::Match(in); |
| 124 if (!headMatch) { |
| 125 return nullptr; |
| 126 } |
| 127 |
| 128 const auto tailMatch = Seq<Es...>::Match(headMatch.fNext); |
| 129 return tailMatch ? MatchT(tailMatch.fNext, V(*headMatch, *tailMatch)) |
| 130 : nullptr; |
| 131 } |
| 132 }; |
| 133 |
| 134 /** |
| 135 * Ordered choice operator (e1|e2). |
| 136 * |
| 137 * Succeeds when either e1 or e2 match (e1 is tried first, then e2). |
| 138 * |
| 139 * The (optional) match results are stored in |v1|, |v2|. |
| 140 * |
| 141 */ |
| 142 template <typename E1, typename E2> |
| 143 struct Choice { |
| 144 struct V { |
| 145 V (const typename E1::V* v1, const typename E2::V* v2) : v1(v1), v2(v2) |
| 146 { |
| 147 SkASSERT(!v1 || !v2); |
| 148 } |
| 149 |
| 150 SkTLazy<typename E1::V> v1; |
| 151 SkTLazy<typename E2::V> v2; |
| 152 }; |
| 153 using MatchT = MatchResult<V>; |
| 154 |
| 155 static MatchT Match(const char* in) { |
| 156 if (const auto m1 = E1::Match(in)) { |
| 157 return MatchT(m1.fNext, V(m1.fValue.get(), nullptr)); |
| 158 } |
| 159 if (const auto m2 = E2::Match(in)) { |
| 160 return MatchT(m2.fNext, V(nullptr, m2.fValue.get())); |
| 161 } |
| 162 return nullptr; |
| 163 } |
| 164 }; |
| 165 |
| 166 /** |
| 167 * Zero-or-more operator (e*). Always succeeds. |
| 168 * |
| 169 * Matches e greedily, and stores the match results in |fValues|. |
| 170 * |
| 171 */ |
| 172 template <typename E> |
| 173 struct Any { |
| 174 struct V { |
| 175 V(SkTArray<typename E::V>&& vs) : fValues(vs) {} |
| 176 |
| 177 SkTArray<typename E::V> fValues; |
| 178 }; |
| 179 using MatchT = MatchResult<V>; |
| 180 |
| 181 static MatchT Match(const char* in) { |
| 182 SkTArray<typename E::V> values; |
| 183 while (const auto m = E::Match(in)) { |
| 184 in = m.fNext; |
| 185 values.push_back(*m); |
| 186 } |
| 187 return MatchT(in, std::move(values)); |
| 188 } |
| 189 }; |
| 190 |
| 191 /** |
| 192 * One-or-more operator (e+). |
| 193 * |
| 194 * Same as zero-or-more, except it fails if e doesn't match at least once. |
| 195 * |
| 196 */ |
| 197 template <typename E> |
| 198 using Some = Seq<E, Any<E>>; |
| 199 |
| 200 /** |
| 201 * End-of-string atom. Matches \0. |
| 202 */ |
| 203 struct EOS { |
| 204 struct V {}; |
| 205 using MatchT = MatchResult<V>; |
| 206 |
| 207 static MatchT Match(const char* in) { |
| 208 return (*in != '\0') ? nullptr : MatchT(in, V()); |
| 209 } |
| 210 }; |
| 211 |
| 212 |
| 213 /** |
| 214 * Literal atom. Matches a list of char literals. |
| 215 */ |
| 216 template <char... Cs> struct LIT; |
| 217 |
| 218 template <> |
| 219 struct LIT<> { |
| 220 struct V {}; |
| 221 using MatchT = MatchResult<V>; |
| 222 |
| 223 static MatchT Match(const char* in) { |
| 224 return MatchT(in, V()); |
| 225 } |
| 226 }; |
| 227 |
| 228 template <char C, char... Cs> |
| 229 struct LIT<C, Cs...> { |
| 230 struct V {}; |
| 231 using MatchT = MatchResult<V>; |
| 232 |
| 233 static MatchT Match(const char* in) { |
| 234 if (*in != C) { |
| 235 return nullptr; |
| 236 } |
| 237 const auto m = LIT<Cs...>::Match(in + 1); |
| 238 return m ? MatchT(m.fNext, V()) : nullptr; |
| 239 } |
| 240 }; |
| 241 |
| 242 } // skpeg ns |
| 243 |
| 244 #endif // SkPEG_DEFINED |
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