⚡ keys are now returned as const reference #1098

nlohmann · May 26, 2018 · 90eb0a9 · 90eb0a9
1 parent 4639bb2
commit 90eb0a9
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Showing 3 changed files with 30 additions and 10 deletions.
diff --git a/include/nlohmann/detail/iterators/iter_impl.hpp b/include/nlohmann/detail/iterators/iter_impl.hpp
@@ -583,7 +583,7 @@ class iter_impl
  @brief return the key of an object iterator
  @pre The iterator is initialized; i.e. `m_object != nullptr`.
  */
- typename object_t::key_type key() const
+ const typename object_t::key_type& key() const
  {
  assert(m_object != nullptr);
 

diff --git a/include/nlohmann/detail/iterators/iteration_proxy.hpp b/include/nlohmann/detail/iterators/iteration_proxy.hpp
@@ -21,6 +21,10 @@ template<typename IteratorType> class iteration_proxy
  IteratorType anchor;
  /// an index for arrays (used to create key names)
  std::size_t array_index = 0;
+ /// a string representation of the array index
+ 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) {}
@@ -35,7 +39,13 @@ template<typename IteratorType> class iteration_proxy
  iteration_proxy_internal& operator++()
  {
  ++anchor;
- ++array_index;
+
+ assert(anchor.m_object != nullptr);
+ if (anchor.m_object->is_array())
+ {
+ // update array index and string representation
+ array_index_str = std::to_string(++array_index);
+ }
 
  return *this;
  }
@@ -47,23 +57,23 @@ template<typename IteratorType> class iteration_proxy
  }
 
  /// return key of the iterator
- std::string key() const
+ 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:
- return std::to_string(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 "";
+ return empty_str;
  }
  }
 

diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
@@ -4636,7 +4636,7 @@ class iter_impl
  @brief return the key of an object iterator
  @pre The iterator is initialized; i.e. `m_object != nullptr`.
  */
- typename object_t::key_type key() const
+ const typename object_t::key_type& key() const
  {
  assert(m_object != nullptr);
 
@@ -4691,6 +4691,10 @@ template<typename IteratorType> class iteration_proxy
  IteratorType anchor;
  /// an index for arrays (used to create key names)
  std::size_t array_index = 0;
+ /// a string representation of the array index
+ 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) {}
@@ -4705,7 +4709,13 @@ template<typename IteratorType> class iteration_proxy
  iteration_proxy_internal& operator++()
  {
  ++anchor;
- ++array_index;
+
+ assert(anchor.m_object != nullptr);
+ if (anchor.m_object->is_array())
+ {
+ // update array index and string representation
+ array_index_str = std::to_string(++array_index);
+ }
 
  return *this;
  }
@@ -4717,23 +4727,23 @@ template<typename IteratorType> class iteration_proxy
  }
 
  /// return key of the iterator
- std::string key() const
+ 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:
- return std::to_string(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 "";
+ return empty_str;
  }
  }