404 lines
11 KiB
C++
404 lines
11 KiB
C++
/*
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* Copyright 2012-present Facebook, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// @author Nicholas Ormrod <njormrod@fb.com>
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#pragma once
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#include <iterator>
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#include <type_traits>
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#include <boost/iterator/iterator_adaptor.hpp>
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#include <boost/mpl/has_xxx.hpp>
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#include <folly/Likely.h>
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#include <folly/Optional.h>
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#include <folly/Traits.h>
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#include <folly/dynamic.h>
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namespace folly {
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template <typename T>
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T convertTo(const dynamic&);
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template <typename T>
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dynamic toDynamic(const T&);
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} // namespace folly
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/**
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* convertTo returns a well-typed representation of the input dynamic.
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*
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* Example:
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*
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* dynamic d = dynamic::array(
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* dynamic::array(1, 2, 3),
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* dynamic::array(4, 5)); // a vector of vector of int
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* auto vvi = convertTo<fbvector<fbvector<int>>>(d);
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*
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* See docs/DynamicConverter.md for supported types and customization
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*/
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namespace folly {
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///////////////////////////////////////////////////////////////////////////////
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// traits
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namespace dynamicconverter_detail {
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BOOST_MPL_HAS_XXX_TRAIT_DEF(value_type)
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BOOST_MPL_HAS_XXX_TRAIT_DEF(iterator)
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BOOST_MPL_HAS_XXX_TRAIT_DEF(mapped_type)
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BOOST_MPL_HAS_XXX_TRAIT_DEF(key_type)
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template <typename T>
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struct iterator_class_is_container {
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typedef std::reverse_iterator<typename T::iterator> some_iterator;
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enum {
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value = has_value_type<T>::value &&
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std::is_constructible<T, some_iterator, some_iterator>::value
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};
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};
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template <typename T>
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using class_is_container =
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Conjunction<has_iterator<T>, iterator_class_is_container<T>>;
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template <typename T>
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using is_range = StrictConjunction<has_value_type<T>, has_iterator<T>>;
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template <typename T>
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using is_container = StrictConjunction<std::is_class<T>, class_is_container<T>>;
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template <typename T>
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using is_map = StrictConjunction<is_range<T>, has_mapped_type<T>>;
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template <typename T>
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using is_associative = StrictConjunction<is_range<T>, has_key_type<T>>;
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} // namespace dynamicconverter_detail
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///////////////////////////////////////////////////////////////////////////////
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// custom iterators
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/**
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* We have iterators that dereference to dynamics, but need iterators
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* that dereference to typename T.
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*
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* Implementation details:
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* 1. We cache the value of the dereference operator. This is necessary
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* because boost::iterator_adaptor requires *it to return a
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* reference.
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* 2. For const reasons, we cannot call operator= to refresh the
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* cache: we must call the destructor then placement new.
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*/
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namespace dynamicconverter_detail {
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template <typename T>
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struct Dereferencer {
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static inline void derefToCache(
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Optional<T>* /* mem */,
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const dynamic::const_item_iterator& /* it */) {
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throw TypeError("array", dynamic::Type::OBJECT);
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}
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static inline void derefToCache(
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Optional<T>* mem,
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const dynamic::const_iterator& it) {
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mem->emplace(convertTo<T>(*it));
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}
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};
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template <typename F, typename S>
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struct Dereferencer<std::pair<F, S>> {
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static inline void derefToCache(
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Optional<std::pair<F, S>>* mem,
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const dynamic::const_item_iterator& it) {
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mem->emplace(convertTo<F>(it->first), convertTo<S>(it->second));
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}
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// Intentional duplication of the code in Dereferencer
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template <typename T>
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static inline void derefToCache(
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Optional<T>* mem,
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const dynamic::const_iterator& it) {
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mem->emplace(convertTo<T>(*it));
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}
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};
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template <typename T, typename It>
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class Transformer
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: public boost::
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iterator_adaptor<Transformer<T, It>, It, typename T::value_type> {
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friend class boost::iterator_core_access;
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typedef typename T::value_type ttype;
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mutable Optional<ttype> cache_;
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void increment() {
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++this->base_reference();
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cache_ = none;
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}
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ttype& dereference() const {
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if (!cache_) {
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Dereferencer<ttype>::derefToCache(&cache_, this->base_reference());
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}
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return cache_.value();
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}
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public:
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explicit Transformer(const It& it) : Transformer::iterator_adaptor_(it) {}
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};
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// conversion factory
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template <typename T, typename It>
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inline std::move_iterator<Transformer<T, It>> conversionIterator(const It& it) {
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return std::make_move_iterator(Transformer<T, It>(it));
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}
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} // namespace dynamicconverter_detail
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///////////////////////////////////////////////////////////////////////////////
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// DynamicConverter specializations
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/**
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* Each specialization of DynamicConverter has the function
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* 'static T convert(const dynamic&);'
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*/
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// default - intentionally unimplemented
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template <typename T, typename Enable = void>
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struct DynamicConverter;
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// boolean
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template <>
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struct DynamicConverter<bool> {
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static bool convert(const dynamic& d) {
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return d.asBool();
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}
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};
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// integrals
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template <typename T>
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struct DynamicConverter<
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T,
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typename std::enable_if<
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std::is_integral<T>::value && !std::is_same<T, bool>::value>::type> {
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static T convert(const dynamic& d) {
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return folly::to<T>(d.asInt());
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}
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};
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// enums
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template <typename T>
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struct DynamicConverter<
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T,
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typename std::enable_if<std::is_enum<T>::value>::type> {
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static T convert(const dynamic& d) {
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using type = typename std::underlying_type<T>::type;
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return static_cast<T>(DynamicConverter<type>::convert(d));
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}
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};
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// floating point
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template <typename T>
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struct DynamicConverter<
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T,
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typename std::enable_if<std::is_floating_point<T>::value>::type> {
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static T convert(const dynamic& d) {
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return folly::to<T>(d.asDouble());
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}
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};
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// fbstring
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template <>
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struct DynamicConverter<folly::fbstring> {
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static folly::fbstring convert(const dynamic& d) {
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return d.asString();
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}
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};
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// std::string
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template <>
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struct DynamicConverter<std::string> {
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static std::string convert(const dynamic& d) {
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return d.asString();
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}
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};
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// std::pair
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template <typename F, typename S>
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struct DynamicConverter<std::pair<F, S>> {
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static std::pair<F, S> convert(const dynamic& d) {
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if (d.isArray() && d.size() == 2) {
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return std::make_pair(convertTo<F>(d[0]), convertTo<S>(d[1]));
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} else if (d.isObject() && d.size() == 1) {
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auto it = d.items().begin();
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return std::make_pair(convertTo<F>(it->first), convertTo<S>(it->second));
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} else {
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throw TypeError("array (size 2) or object (size 1)", d.type());
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}
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}
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};
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// non-associative containers
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template <typename C>
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struct DynamicConverter<
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C,
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typename std::enable_if<
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dynamicconverter_detail::is_container<C>::value &&
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!dynamicconverter_detail::is_associative<C>::value>::type> {
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static C convert(const dynamic& d) {
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if (d.isArray()) {
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return C(
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dynamicconverter_detail::conversionIterator<C>(d.begin()),
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dynamicconverter_detail::conversionIterator<C>(d.end()));
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} else if (d.isObject()) {
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return C(
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dynamicconverter_detail::conversionIterator<C>(d.items().begin()),
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dynamicconverter_detail::conversionIterator<C>(d.items().end()));
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} else {
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throw TypeError("object or array", d.type());
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}
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}
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};
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// associative containers
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template <typename C>
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struct DynamicConverter<
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C,
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typename std::enable_if<
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dynamicconverter_detail::is_container<C>::value &&
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dynamicconverter_detail::is_associative<C>::value>::type> {
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static C convert(const dynamic& d) {
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C ret; // avoid direct initialization due to unordered_map's constructor
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// causing memory corruption if the iterator throws an exception
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if (d.isArray()) {
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ret.insert(
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dynamicconverter_detail::conversionIterator<C>(d.begin()),
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dynamicconverter_detail::conversionIterator<C>(d.end()));
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} else if (d.isObject()) {
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ret.insert(
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dynamicconverter_detail::conversionIterator<C>(d.items().begin()),
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dynamicconverter_detail::conversionIterator<C>(d.items().end()));
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} else {
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throw TypeError("object or array", d.type());
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}
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return ret;
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}
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};
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///////////////////////////////////////////////////////////////////////////////
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// DynamicConstructor specializations
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/**
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* Each specialization of DynamicConstructor has the function
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* 'static dynamic construct(const C&);'
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*/
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// default
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template <typename C, typename Enable = void>
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struct DynamicConstructor {
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static dynamic construct(const C& x) {
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return dynamic(x);
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}
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};
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// identity
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template <typename C>
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struct DynamicConstructor<
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C,
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typename std::enable_if<std::is_same<C, dynamic>::value>::type> {
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static dynamic construct(const C& x) {
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return x;
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}
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};
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// maps
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template <typename C>
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struct DynamicConstructor<
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C,
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typename std::enable_if<
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!std::is_same<C, dynamic>::value &&
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dynamicconverter_detail::is_map<C>::value>::type> {
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static dynamic construct(const C& x) {
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dynamic d = dynamic::object;
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for (const auto& pair : x) {
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d.insert(toDynamic(pair.first), toDynamic(pair.second));
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}
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return d;
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}
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};
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// other ranges
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template <typename C>
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struct DynamicConstructor<
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C,
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typename std::enable_if<
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!std::is_same<C, dynamic>::value &&
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!dynamicconverter_detail::is_map<C>::value &&
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!std::is_constructible<StringPiece, const C&>::value &&
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dynamicconverter_detail::is_range<C>::value>::type> {
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static dynamic construct(const C& x) {
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dynamic d = dynamic::array;
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for (const auto& item : x) {
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d.push_back(toDynamic(item));
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}
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return d;
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}
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};
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// pair
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template <typename A, typename B>
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struct DynamicConstructor<std::pair<A, B>, void> {
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static dynamic construct(const std::pair<A, B>& x) {
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dynamic d = dynamic::array;
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d.push_back(toDynamic(x.first));
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d.push_back(toDynamic(x.second));
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return d;
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}
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};
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// vector<bool>
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template <>
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struct DynamicConstructor<std::vector<bool>, void> {
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static dynamic construct(const std::vector<bool>& x) {
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dynamic d = dynamic::array;
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// Intentionally specifying the type as bool here.
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// std::vector<bool>'s iterators return a proxy which is a prvalue
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// and hence cannot bind to an lvalue reference such as auto&
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for (bool item : x) {
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d.push_back(toDynamic(item));
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}
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return d;
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}
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};
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///////////////////////////////////////////////////////////////////////////////
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// implementation
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template <typename T>
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T convertTo(const dynamic& d) {
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return DynamicConverter<typename std::remove_cv<T>::type>::convert(d);
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}
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template <typename T>
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dynamic toDynamic(const T& x) {
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return DynamicConstructor<typename std::remove_cv<T>::type>::construct(x);
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}
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} // namespace folly
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