mirror of
https://github.com/ecency/ecency-mobile.git
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356 lines
9.4 KiB
C++
356 lines
9.4 KiB
C++
/*
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* Copyright 2016 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 <folly/dynamic.h>
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namespace folly {
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template <typename T> T convertTo(const dynamic&);
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template <typename T> dynamic toDynamic(const T&);
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}
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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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#include <type_traits>
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#include <iterator>
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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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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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template <typename T> struct iterator_class_is_container {
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typedef std::reverse_iterator<typename T::iterator> some_iterator;
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enum { 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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template <typename T>
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using class_is_container = typename
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std::conditional<
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has_iterator<T>::value,
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iterator_class_is_container<T>,
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std::false_type
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>::type;
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template <typename T> struct class_is_range {
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enum { value = has_value_type<T>::value &&
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has_iterator<T>::value };
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};
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template <typename T> struct is_container
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: std::conditional<
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std::is_class<T>::value,
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class_is_container<T>,
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std::false_type
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>::type {};
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template <typename T> struct is_range
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: std::conditional<
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std::is_class<T>::value,
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class_is_range<T>,
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std::false_type
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>::type {};
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template <typename T> struct is_map
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: std::integral_constant<
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bool,
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is_range<T>::value && has_mapped_type<T>::value
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> {};
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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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T* /* mem */, 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(T* mem, const dynamic::const_iterator& it) {
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new (mem) T(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
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derefToCache(std::pair<F, S>* mem, const dynamic::const_item_iterator& it) {
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new (mem) std::pair<F, S>(
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convertTo<F>(it->first), convertTo<S>(it->second)
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);
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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(T* mem, const dynamic::const_iterator& it) {
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new (mem) T(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 : public boost::iterator_adaptor<
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Transformer<T, It>,
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It,
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typename T::value_type
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> {
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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 ttype cache_;
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mutable bool valid_;
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void increment() {
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++this->base_reference();
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valid_ = false;
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}
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ttype& dereference() const {
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if (LIKELY(!valid_)) {
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cache_.~ttype();
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Dereferencer<ttype>::derefToCache(&cache_, this->base_reference());
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valid_ = true;
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}
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return cache_;
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}
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public:
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explicit Transformer(const It& it)
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: Transformer::iterator_adaptor_(it), valid_(false) {}
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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>>
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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> 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<T,
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typename std::enable_if<std::is_integral<T>::value &&
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!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<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<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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// containers
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template <typename C>
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struct DynamicConverter<C,
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typename std::enable_if<
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dynamicconverter_detail::is_container<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(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(dynamicconverter_detail::conversionIterator<C>
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(d.items().begin()),
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dynamicconverter_detail::conversionIterator<C>
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(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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///////////////////////////////////////////////////////////////////////////////
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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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// maps
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template<typename C>
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struct DynamicConstructor<C,
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typename std::enable_if<
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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 (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<C,
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typename std::enable_if<
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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 (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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///////////////////////////////////////////////////////////////////////////////
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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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