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Merge pull request #1391 from pratikpc/develop

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Added Support for Structured Bindings
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Niels Lohmann 2018-12-20 08:58:08 +01:00 • committed by GitHub
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6 changed files with 337 additions and 248 deletions
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8
include/nlohmann/detail/iterators/iter_impl.hpp
View file

@ -17,24 +17,21 @@ namespace detail
{
// forward declare, to be able to friend it later on
template<typename IteratorType> class iteration_proxy;
template<typename IteratorType> class iteration_proxy_value;
/*!
@brief a template for a bidirectional iterator for the @ref basic_json class
This class implements a both iterators (iterator and const_iterator) for the
@ref basic_json class.
@note An iterator is called *initialized* when a pointer to a JSON value has
been set (e.g., by a constructor or a copy assignment). If the iterator is
default-constructed, it is *uninitialized* and most methods are undefined.
**The library uses assertions to detect calls on uninitialized iterators.**
@requirement The class satisfies the following concept requirements:
-
[BidirectionalIterator](https://en.cppreference.com/w/cpp/named_req/BidirectionalIterator):
The iterator that can be moved can be moved in both directions (i.e.
incremented and decremented).
@since version 1.0.0, simplified in version 2.0.9, change to bidirectional
iterators in version 3.0.0 (see https://github.com/nlohmann/json/issues/593)
*/
@ -45,6 +42,7 @@ class iter_impl
friend iter_impl<typename std::conditional<std::is_const<BasicJsonType>::value, typename std::remove_const<BasicJsonType>::type, const BasicJsonType>::type>;
friend BasicJsonType;
friend iteration_proxy<iter_impl>;
friend iteration_proxy_value<iter_impl>;
using object_t = typename BasicJsonType::object_t;
using array_t = typename BasicJsonType::array_t;
@ -611,4 +609,4 @@ class iter_impl
internal_iterator<typename std::remove_const<BasicJsonType>::type> m_it;
};
} // namespace detail
} // namespace nlohmann
} // namespace nlohmann

219
include/nlohmann/detail/iterators/iteration_proxy.hpp
View file

@ -3,104 +3,105 @@
#include <cstddef> // size_t
#include <string> // string, to_string
#include <iterator> // input_iterator_tag
#include <tuple> // tuple_size, get, tuple_element
#include <nlohmann/detail/value_t.hpp>
#include <nlohmann/detail/meta/type_traits.hpp>
namespace nlohmann
{
namespace detail
{
template <typename IteratorType> class iteration_proxy_value
{
public:
using difference_type = std::ptrdiff_t;
using value_type = iteration_proxy_value;
using pointer = value_type * ;
using reference = value_type & ;
using iterator_category = std::input_iterator_tag;
private:
/// the iterator
IteratorType anchor;
/// an index for arrays (used to create key names)
std::size_t array_index = 0;
/// last stringified array index
mutable std::size_t array_index_last = 0;
/// a string representation of the array index
mutable std::string array_index_str = "0";
/// an empty string (to return a reference for primitive values)
const std::string empty_str = "";
public:
explicit iteration_proxy_value(IteratorType it) noexcept : anchor(it) {}
/// dereference operator (needed for range-based for)
iteration_proxy_value& operator*()
{
return *this;
}
/// increment operator (needed for range-based for)
iteration_proxy_value& operator++()
{
++anchor;
++array_index;
return *this;
}
/// equality operator (needed for InputIterator)
bool operator==(const iteration_proxy_value& o) const noexcept
{
return anchor == o.anchor;
}
/// inequality operator (needed for range-based for)
bool operator!=(const iteration_proxy_value& o) const noexcept
{
return anchor != o.anchor;
}
/// return key of the iterator
const std::string& key() const
{
assert(anchor.m_object != nullptr);
switch (anchor.m_object->type())
{
// use integer array index as key
case value_t::array:
{
if (array_index != array_index_last)
{
array_index_str = std::to_string(array_index);
array_index_last = array_index;
}
return array_index_str;
}
// use key from the object
case value_t::object:
return anchor.key();
// use an empty key for all primitive types
default:
return empty_str;
}
}
/// return value of the iterator
typename IteratorType::reference value() const
{
return anchor.value();
}
};
/// proxy class for the items() function
template<typename IteratorType> class iteration_proxy
{
private:
/// helper class for iteration
class iteration_proxy_internal
{
public:
using difference_type = std::ptrdiff_t;
using value_type = iteration_proxy_internal;
using pointer = iteration_proxy_internal*;
using reference = iteration_proxy_internal&;
using iterator_category = std::input_iterator_tag;
private:
/// the iterator
IteratorType anchor;
/// an index for arrays (used to create key names)
std::size_t array_index = 0;
/// last stringified array index
mutable std::size_t array_index_last = 0;
/// a string representation of the array index
mutable std::string array_index_str = "0";
/// an empty string (to return a reference for primitive values)
const std::string empty_str = "";
public:
explicit iteration_proxy_internal(IteratorType it) noexcept : anchor(it) {}
/// dereference operator (needed for range-based for)
iteration_proxy_internal& operator*()
{
return *this;
}
/// increment operator (needed for range-based for)
iteration_proxy_internal& operator++()
{
++anchor;
++array_index;
return *this;
}
/// equality operator (needed for InputIterator)
bool operator==(const iteration_proxy_internal& o) const noexcept
{
return anchor == o.anchor;
}
/// inequality operator (needed for range-based for)
bool operator!=(const iteration_proxy_internal& o) const noexcept
{
return anchor != o.anchor;
}
/// return key of the iterator
const std::string& key() const
{
assert(anchor.m_object != nullptr);
switch (anchor.m_object->type())
{
// use integer array index as key
case value_t::array:
{
if (array_index != array_index_last)
{
array_index_str = std::to_string(array_index);
array_index_last = array_index;
}
return array_index_str;
}
// use key from the object
case value_t::object:
return anchor.key();
// use an empty key for all primitive types
default:
return empty_str;
}
}
/// return value of the iterator
typename IteratorType::reference value() const
{
return anchor.value();
}
};
/// the container to iterate
typename IteratorType::reference container;
@ -110,16 +111,52 @@ template<typename IteratorType> class iteration_proxy
: container(cont) {}
/// return iterator begin (needed for range-based for)
iteration_proxy_internal begin() noexcept
iteration_proxy_value<IteratorType> begin() noexcept
{
return iteration_proxy_internal(container.begin());
return iteration_proxy_value<IteratorType>(container.begin());
}
/// return iterator end (needed for range-based for)
iteration_proxy_internal end() noexcept
iteration_proxy_value<IteratorType> end() noexcept
{
return iteration_proxy_internal(container.end());
return iteration_proxy_value<IteratorType>(container.end());
}
};
// Structured Bindings Support
// For further reference see https://blog.tartanllama.xyz/structured-bindings/
// And see https://github.com/nlohmann/json/pull/1391
template <std::size_t N, typename IteratorType, enable_if_t<N == 0, int> = 0>
auto get(const nlohmann::detail::iteration_proxy_value<IteratorType>& i) -> decltype(i.key())
{
return i.key();
}
// Structured Bindings Support
// For further reference see https://blog.tartanllama.xyz/structured-bindings/
// And see https://github.com/nlohmann/json/pull/1391
template <std::size_t N, typename IteratorType, enable_if_t<N == 1, int> = 0>
auto get(const nlohmann::detail::iteration_proxy_value<IteratorType>& i) -> decltype(i.value())
{
return i.value();
}
} // namespace detail
} // namespace nlohmann
// The Addition to the STD Namespace is required to add
// Structured Bindings Support to the iteration_proxy_value class
// For further reference see https://blog.tartanllama.xyz/structured-bindings/
// And see https://github.com/nlohmann/json/pull/1391
namespace std
{
template <typename IteratorType>
struct tuple_size<::nlohmann::detail::iteration_proxy_value<IteratorType>>
: std::integral_constant<std::size_t, 2> {};
template <std::size_t N, typename IteratorType>
struct tuple_element <
N, ::nlohmann::detail::iteration_proxy_value<IteratorType >>
{
using type = decltype(
get<N>(std::declval <
::nlohmann::detail::iteration_proxy_value<IteratorType >> ()));
};
}