2 * Copyright 2016 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 // @author Nicholas Ormrod <njormrod@fb.com>
19 #ifndef DYNAMIC_CONVERTER_H
20 #define DYNAMIC_CONVERTER_H
22 #include <folly/dynamic.h>
24 template <typename T> T convertTo(const dynamic&);
25 template <typename T> dynamic toDynamic(const T&);
29 * convertTo returns a well-typed representation of the input dynamic.
33 * dynamic d = { { 1, 2, 3 }, { 4, 5 } }; // a vector of vector of int
34 * auto vvi = convertTo<fbvector<fbvector<int>>>(d);
36 * See docs/DynamicConverter.md for supported types and customization
40 #include <type_traits>
42 #include <boost/iterator/iterator_adaptor.hpp>
43 #include <boost/mpl/has_xxx.hpp>
44 #include <folly/Likely.h>
48 ///////////////////////////////////////////////////////////////////////////////
51 namespace dynamicconverter_detail {
53 BOOST_MPL_HAS_XXX_TRAIT_DEF(value_type);
54 BOOST_MPL_HAS_XXX_TRAIT_DEF(iterator);
55 BOOST_MPL_HAS_XXX_TRAIT_DEF(mapped_type);
57 template <typename T> struct iterator_class_is_container {
58 typedef std::reverse_iterator<typename T::iterator> some_iterator;
59 enum { value = has_value_type<T>::value &&
60 std::is_constructible<T, some_iterator, some_iterator>::value };
64 using class_is_container = typename
66 has_iterator<T>::value,
67 iterator_class_is_container<T>,
71 template <typename T> struct class_is_range {
72 enum { value = has_value_type<T>::value &&
73 has_iterator<T>::value };
77 template <typename T> struct is_container
79 std::is_class<T>::value,
80 class_is_container<T>,
84 template <typename T> struct is_range
86 std::is_class<T>::value,
91 template <typename T> struct is_map
92 : std::integral_constant<
94 is_range<T>::value && has_mapped_type<T>::value
97 } // namespace dynamicconverter_detail
99 ///////////////////////////////////////////////////////////////////////////////
103 * We have iterators that dereference to dynamics, but need iterators
104 * that dereference to typename T.
106 * Implementation details:
107 * 1. We cache the value of the dereference operator. This is necessary
108 * because boost::iterator_adaptor requires *it to return a
110 * 2. For const reasons, we cannot call operator= to refresh the
111 * cache: we must call the destructor then placement new.
114 namespace dynamicconverter_detail {
117 struct Dereferencer {
118 static inline void derefToCache(
119 T* /* mem */, const dynamic::const_item_iterator& /* it */) {
120 throw TypeError("array", dynamic::Type::OBJECT);
123 static inline void derefToCache(T* mem, const dynamic::const_iterator& it) {
124 new (mem) T(convertTo<T>(*it));
128 template<typename F, typename S>
129 struct Dereferencer<std::pair<F, S>> {
131 derefToCache(std::pair<F, S>* mem, const dynamic::const_item_iterator& it) {
132 new (mem) std::pair<F, S>(
133 convertTo<F>(it->first), convertTo<S>(it->second)
137 // Intentional duplication of the code in Dereferencer
138 template <typename T>
139 static inline void derefToCache(T* mem, const dynamic::const_iterator& it) {
140 new (mem) T(convertTo<T>(*it));
144 template <typename T, typename It>
145 class Transformer : public boost::iterator_adaptor<
148 typename T::value_type
150 friend class boost::iterator_core_access;
152 typedef typename T::value_type ttype;
154 mutable ttype cache_;
158 ++this->base_reference();
162 ttype& dereference() const {
163 if (LIKELY(!valid_)) {
165 Dereferencer<ttype>::derefToCache(&cache_, this->base_reference());
172 explicit Transformer(const It& it)
173 : Transformer::iterator_adaptor_(it), valid_(false) {}
176 // conversion factory
177 template <typename T, typename It>
178 inline std::move_iterator<Transformer<T, It>>
179 conversionIterator(const It& it) {
180 return std::make_move_iterator(Transformer<T, It>(it));
183 } // namespace dynamicconverter_detail
185 ///////////////////////////////////////////////////////////////////////////////
186 // DynamicConverter specializations
189 * Each specialization of DynamicConverter has the function
190 * 'static T convert(const dynamic&);'
193 // default - intentionally unimplemented
194 template <typename T, typename Enable = void> struct DynamicConverter;
198 struct DynamicConverter<bool> {
199 static bool convert(const dynamic& d) {
205 template <typename T>
206 struct DynamicConverter<T,
207 typename std::enable_if<std::is_integral<T>::value &&
208 !std::is_same<T, bool>::value>::type> {
209 static T convert(const dynamic& d) {
210 return folly::to<T>(d.asInt());
215 template <typename T>
216 struct DynamicConverter<T,
217 typename std::enable_if<std::is_enum<T>::value>::type> {
218 static T convert(const dynamic& d) {
219 using type = typename std::underlying_type<T>::type;
220 return static_cast<T>(DynamicConverter<type>::convert(d));
225 template <typename T>
226 struct DynamicConverter<T,
227 typename std::enable_if<std::is_floating_point<T>::value>::type> {
228 static T convert(const dynamic& d) {
229 return folly::to<T>(d.asDouble());
235 struct DynamicConverter<folly::fbstring> {
236 static folly::fbstring convert(const dynamic& d) {
243 struct DynamicConverter<std::string> {
244 static std::string convert(const dynamic& d) {
245 return d.asString().toStdString();
250 template <typename F, typename S>
251 struct DynamicConverter<std::pair<F,S>> {
252 static std::pair<F, S> convert(const dynamic& d) {
253 if (d.isArray() && d.size() == 2) {
254 return std::make_pair(convertTo<F>(d[0]), convertTo<S>(d[1]));
255 } else if (d.isObject() && d.size() == 1) {
256 auto it = d.items().begin();
257 return std::make_pair(convertTo<F>(it->first), convertTo<S>(it->second));
259 throw TypeError("array (size 2) or object (size 1)", d.type());
265 template <typename C>
266 struct DynamicConverter<C,
267 typename std::enable_if<
268 dynamicconverter_detail::is_container<C>::value>::type> {
269 static C convert(const dynamic& d) {
271 return C(dynamicconverter_detail::conversionIterator<C>(d.begin()),
272 dynamicconverter_detail::conversionIterator<C>(d.end()));
273 } else if (d.isObject()) {
274 return C(dynamicconverter_detail::conversionIterator<C>
276 dynamicconverter_detail::conversionIterator<C>
279 throw TypeError("object or array", d.type());
284 ///////////////////////////////////////////////////////////////////////////////
285 // DynamicConstructor specializations
288 * Each specialization of DynamicConstructor has the function
289 * 'static dynamic construct(const C&);'
293 template <typename C, typename Enable = void>
294 struct DynamicConstructor {
295 static dynamic construct(const C& x) {
302 struct DynamicConstructor<C,
303 typename std::enable_if<
304 dynamicconverter_detail::is_map<C>::value>::type> {
305 static dynamic construct(const C& x) {
306 dynamic d = dynamic::object;
307 for (auto& pair : x) {
308 d.insert(toDynamic(pair.first), toDynamic(pair.second));
316 struct DynamicConstructor<C,
317 typename std::enable_if<
318 !dynamicconverter_detail::is_map<C>::value &&
319 !std::is_constructible<StringPiece, const C&>::value &&
320 dynamicconverter_detail::is_range<C>::value>::type> {
321 static dynamic construct(const C& x) {
323 for (auto& item : x) {
324 d.push_back(toDynamic(item));
331 template<typename A, typename B>
332 struct DynamicConstructor<std::pair<A, B>, void> {
333 static dynamic construct(const std::pair<A, B>& x) {
335 d.push_back(toDynamic(x.first));
336 d.push_back(toDynamic(x.second));
341 ///////////////////////////////////////////////////////////////////////////////
344 template <typename T>
345 T convertTo(const dynamic& d) {
346 return DynamicConverter<typename std::remove_cv<T>::type>::convert(d);
350 dynamic toDynamic(const T& x) {
351 return DynamicConstructor<typename std::remove_cv<T>::type>::construct(x);
356 #endif // DYNAMIC_CONVERTER_H