Merge branch 'develop' into fix/1237

.github/CONTRIBUTING.md

@@ -54,7 +54,7 @@ To make changes, you need to edit the following files:
 
 ## Please don't
 
-- The C++11 support varies between different **compilers** and versions. Please note the [list of supported compilers](https://github.com/nlohmann/json/blob/master/README.md#supported-compilers). Some compilers like GCC 4.8 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with `#ifdef`s or other means.
+- The C++11 support varies between different **compilers** and versions. Please note the [list of supported compilers](https://github.com/nlohmann/json/blob/master/README.md#supported-compilers). Some compilers like GCC 4.7 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with `#ifdef`s or other means.
 - Specifically, I am aware of compilation problems with **Microsoft Visual Studio** (there even is an [issue label](https://github.com/nlohmann/json/issues?utf8=✓&q=label%3A%22visual+studio%22+) for these kind of bugs). I understand that even in 2016, complete C++11 support isn't there yet. But please also understand that I do not want to drop features or uglify the code just to make Microsoft's sub-standard compiler happy. The past has shown that there are ways to express the functionality such that the code compiles with the most recent MSVC - unfortunately, this is not the main objective of the project.
 - Please refrain from proposing changes that would **break [JSON](http://json.org) conformance**. If you propose a conformant extension of JSON to be supported by the library, please motivate this extension.
   - We shall not extend the library to **support comments**. There is quite some [controversy](https://www.reddit.com/r/programming/comments/4v6chu/why_json_doesnt_support_comments_douglas_crockford/) around this topic, and there were quite some [issues](https://github.com/nlohmann/json/issues/376) on this. We believe that JSON is fine without comments.

.github/PULL_REQUEST_TEMPLATE.md

@@ -13,7 +13,7 @@ Read the [Contribution Guidelines](https://github.com/nlohmann/json/blob/develop
 
 ## Please don't
 
-- The C++11 support varies between different **compilers** and versions. Please note the [list of supported compilers](https://github.com/nlohmann/json/blob/master/README.md#supported-compilers). Some compilers like GCC 4.8 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with `#ifdef`s or other means.
+- The C++11 support varies between different **compilers** and versions. Please note the [list of supported compilers](https://github.com/nlohmann/json/blob/master/README.md#supported-compilers). Some compilers like GCC 4.7 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with `#ifdef`s or other means.
 - Specifically, I am aware of compilation problems with **Microsoft Visual Studio** (there even is an [issue label](https://github.com/nlohmann/json/issues?utf8=✓&q=label%3A%22visual+studio%22+) for these kind of bugs). I understand that even in 2016, complete C++11 support isn't there yet. But please also understand that I do not want to drop features or uglify the code just to make Microsoft's sub-standard compiler happy. The past has shown that there are ways to express the functionality such that the code compiles with the most recent MSVC - unfortunately, this is not the main objective of the project.
 - Please refrain from proposing changes that would **break [JSON](http://json.org) conformance**. If you propose a conformant extension of JSON to be supported by the library, please motivate this extension.
 - Please do not open pull requests that address **multiple issues**.

.travis.yml

@@ -168,7 +168,15 @@ matrix:
 
   - os: linux
     compiler: gcc
-    env: COMPILER=g++-4.9
+    env: compiler=g++-4.8
+    addons:
+      apt:
+        sources: ['ubuntu-toolchain-r-test']
+        packages: ['g++-4.8', 'ninja-build']
+
+  - os: linux
+    compiler: gcc
+    env: compiler=g++-4.9
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']

README.md

@@ -227,12 +227,15 @@ json j_string = "this is a string";
 std::string cpp_string = j_string;
 // retrieve the string value (explicit JSON to std::string conversion)
 auto cpp_string2 = j_string.get<std::string>();
+// retrieve the string value (alternative explicit JSON to std::string conversion)
+std::string cpp_string3;
+j_string.get_to(cpp_string3);
 
 // retrieve the serialized value (explicit JSON serialization)
 std::string serialized_string = j_string.dump();
 
 // output of original string
-std::cout << cpp_string << " == " << cpp_string2 << " == " << j_string.get<std::string>() << '\n';
+std::cout << cpp_string << " == " << cpp_string2 << " == " << cpp_string3 << " == " << j_string.get<std::string>() << '\n';
 // output of serialized value
 std::cout << j_string << " == " << serialized_string << std::endl;
 ```
@@ -643,15 +646,15 @@ namespace ns {
     }
 
     void from_json(const json& j, person& p) {
-        p.name = j.at("name").get<std::string>();
+        j.at("name").get_to(p.name);
-        p.address = j.at("address").get<std::string>();
+        j.at("address").get_to(p.address);
-        p.age = j.at("age").get<int>();
+        j.at("age").get_to(p.age);
     }
 } // namespace ns
 ```
 
 That's all! When calling the `json` constructor with your type, your custom `to_json` method will be automatically called.
-Likewise, when calling `get<your_type>()`, the `from_json` method will be called.
+Likewise, when calling `get<your_type>()` or `get_to(your_type&)`, the `from_json` method will be called.
 
 Some important things:
 
@@ -659,9 +662,8 @@ Some important things:
 * Those methods **MUST** be available (e.g., properly headers must be included) everywhere you use the implicit conversions. Look at [issue 1108](https://github.com/nlohmann/json/issues/1108) for errors that may occur otherwise.
 * When using `get<your_type>()`, `your_type` **MUST** be [DefaultConstructible](https://en.cppreference.com/w/cpp/named_req/DefaultConstructible). (There is a way to bypass this requirement described later.)
 * In function `from_json`, use function [`at()`](https://nlohmann.github.io/json/classnlohmann_1_1basic__json_a93403e803947b86f4da2d1fb3345cf2c.html#a93403e803947b86f4da2d1fb3345cf2c) to access the object values rather than `operator[]`. In case a key does not exist, `at` throws an exception that you can handle, whereas `operator[]` exhibits undefined behavior.
-* In case your type contains several `operator=` definitions, code like `your_variable = your_json;` [may not compile](https://github.com/nlohmann/json/issues/667). You need to write `your_variable = your_json.get<decltype your_variable>();` instead.
+* In case your type contains several `operator=` definitions, code like `your_variable = your_json;` [may not compile](https://github.com/nlohmann/json/issues/667). You need to write `your_variable = your_json.get<decltype(your_variable)>();` or `your_json.get_to(your_variable);` instead.
 * You do not need to add serializers or deserializers for STL types like `std::vector`: the library already implements these.
-* Be careful with the definition order of the `from_json`/`to_json` functions: If a type `B` has a member of type `A`, you **MUST** define `to_json(A)` before `to_json(B)`. Look at [issue 561](https://github.com/nlohmann/json/issues/561) for more details.
 
 
 #### How do I convert third-party types?
@@ -843,7 +845,7 @@ json j_from_ubjson = json::from_ubjson(v_ubjson);
 
 Though it's 2018 already, the support for C++11 is still a bit sparse. Currently, the following compilers are known to work:
 
-- GCC 4.9 - 8.2 (and possibly later)
+- GCC 4.8 - 8.2 (and possibly later)
 - Clang 3.4 - 6.1 (and possibly later)
 - Intel C++ Compiler 17.0.2 (and possibly later)
 - Microsoft Visual C++ 2015 / Build Tools 14.0.25123.0 (and possibly later)
@@ -853,7 +855,7 @@ I would be happy to learn about other compilers/versions.
 
 Please note:
 
-- GCC 4.8 does not work because of two bugs ([55817](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55817) and [57824](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57824)) in the C++11 support. Note there is a [pull request](https://github.com/nlohmann/json/pull/212) to fix some of the issues.
+- GCC 4.8 has a bug [57824](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57824)): multiline raw strings cannot be the arguments to macros. Don't use multiline raw strings directly in macros with this compiler.
 - Android defaults to using very old compilers and C++ libraries. To fix this, add the following to your `Application.mk`. This will switch to the LLVM C++ library, the Clang compiler, and enable C++11 and other features disabled by default.
 
     ```
@@ -872,6 +874,7 @@ The following compilers are currently used in continuous integration at [Travis]
 
 | Compiler        | Operating System             | Version String |
 |-----------------|------------------------------|----------------|
+| GCC 4.8.5       | Ubuntu 14.04.5 LTS           | g++-4.8 (Ubuntu 4.8.5-2ubuntu1~14.04.2) 4.8.5 |
 | GCC 4.9.4       | Ubuntu 14.04.1 LTS           | g++-4.9 (Ubuntu 4.9.4-2ubuntu1~14.04.1) 4.9.4 |
 | GCC 5.5.0       | Ubuntu 14.04.1 LTS           | g++-5 (Ubuntu 5.5.0-12ubuntu1~14.04) 5.5.0 20171010 |
 | GCC 6.4.0       | Ubuntu 14.04.1 LTS           | g++-6 (Ubuntu 6.4.0-17ubuntu1~14.04) 6.4.0 20180424 |

doc/examples/get_to.cpp

@@ -0,0 +1,60 @@
+#include <iostream>
+#include <unordered_map>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create a JSON value with different types
+    json json_types =
+    {
+        {"boolean", true},
+        {
+            "number", {
+                {"integer", 42},
+                {"floating-point", 17.23}
+            }
+        },
+        {"string", "Hello, world!"},
+        {"array", {1, 2, 3, 4, 5}},
+        {"null", nullptr}
+    };
+
+    bool v1;
+    int v2;
+    short v3;
+    float v4;
+    int v5;
+    std::string v6;
+    std::vector<short> v7;
+    std::unordered_map<std::string, json> v8;
+
+
+    // use explicit conversions
+    json_types["boolean"].get_to(v1);
+    json_types["number"]["integer"].get_to(v2);
+    json_types["number"]["integer"].get_to(v3);
+    json_types["number"]["floating-point"].get_to(v4);
+    json_types["number"]["floating-point"].get_to(v5);
+    json_types["string"].get_to(v6);
+    json_types["array"].get_to(v7);
+    json_types.get_to(v8);
+
+    // print the conversion results
+    std::cout << v1 << '\n';
+    std::cout << v2 << ' ' << v3 << '\n';
+    std::cout << v4 << ' ' << v5 << '\n';
+    std::cout << v6 << '\n';
+
+    for (auto i : v7)
+    {
+        std::cout << i << ' ';
+    }
+    std::cout << "\n\n";
+
+    for (auto i : v8)
+    {
+        std::cout << i.first << ": " << i.second << '\n';
+    }
+}

doc/examples/get_to.link

@@ -0,0 +1 @@
+<a target="_blank" href="https://wandbox.org/permlink/QxtxaO6JZAMJPutC"><b>online</b></a>

doc/examples/get_to.output

@@ -0,0 +1,11 @@
+1
+42 42
+17.23 17
+Hello, world!
+1 2 3 4 5 
+
+string: "Hello, world!"
+number: {"floating-point":17.23,"integer":42}
+null: null
+boolean: true
+array: [1,2,3,4,5]

include/nlohmann/detail/macro_scope.hpp

@@ -10,7 +10,7 @@
             #error "unsupported Clang version - see https://github.com/nlohmann/json#supported-compilers"
         #endif
     #elif defined(__GNUC__) && !(defined(__ICC) || defined(__INTEL_COMPILER))
-        #if (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) < 40900
+        #if (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) < 40800
             #error "unsupported GCC version - see https://github.com/nlohmann/json#supported-compilers"
         #endif
     #endif

include/nlohmann/detail/output/serializer.hpp

@@ -442,7 +442,7 @@ class serializer
             return;
         }
 
-        const bool is_negative = (x <= 0) and (x != 0);  // see issue #755
+        const bool is_negative = not (x >= 0);  // see issue #755
         std::size_t i = 0;
 
         while (x != 0)

include/nlohmann/json.hpp

@@ -2623,6 +2623,52 @@ class basic_json
         return JSONSerializer<ValueTypeCV>::from_json(*this);
     }
 
+    /*!
+    @brief get a value (explicit)
+
+    Explicit type conversion between the JSON value and a compatible value.
+    The value is filled into the input parameter by calling the @ref json_serializer<ValueType>
+    `from_json()` method.
+
+    The function is equivalent to executing
+    @code {.cpp}
+    ValueType v;
+    JSONSerializer<ValueType>::from_json(*this, v);
+    @endcode
+
+    This overloads is chosen if:
+    - @a ValueType is not @ref basic_json,
+    - @ref json_serializer<ValueType> has a `from_json()` method of the form
+      `void from_json(const basic_json&, ValueType&)`, and
+
+    @tparam ValueType the input parameter type.
+
+    @return the input parameter, allowing chaining calls.
+
+    @throw what @ref json_serializer<ValueType> `from_json()` method throws
+
+    @liveexample{The example below shows several conversions from JSON values
+    to other types. There a few things to note: (1) Floating-point numbers can
+    be converted to integers\, (2) A JSON array can be converted to a standard
+    `std::vector<short>`\, (3) A JSON object can be converted to C++
+    associative containers such as `std::unordered_map<std::string\,
+    json>`.,get_to}
+
+    @since version 3.3.0
+    */
+    template<typename ValueType,
+             detail::enable_if_t <
+                 not detail::is_basic_json<ValueType>::value and
+                 detail::has_from_json<basic_json_t, ValueType>::value,
+                 int> = 0>
+    ValueType & get_to(ValueType& v) const noexcept(noexcept(
+                JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), v)))
+    {
+        JSONSerializer<ValueType>::from_json(*this, v);
+        return v;
+    }
+
+
     /*!
     @brief get a pointer value (implicit)
 
@@ -4915,6 +4961,26 @@ class basic_json
         return {it, res.second};
     }
 
+    /// Helper for insertion of an iterator
+    /// @note: This uses std::distance to support GCC 4.8,
+    ///        see https://github.com/nlohmann/json/pull/1257
+    template<typename... Args>
+    iterator insert_iterator(const_iterator pos, Args&& ... args)
+    {
+        iterator result(this);
+        assert(m_value.array != nullptr);
+
+        auto insert_pos = std::distance(m_value.array->begin(), pos.m_it.array_iterator);
+        m_value.array->insert(pos.m_it.array_iterator, std::forward<Args>(args)...);
+        result.m_it.array_iterator = m_value.array->begin() + insert_pos;
+
+        // This could have been written as:
+        // result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, cnt, val);
+        // but the return value of insert is missing in GCC 4.8, so it is written this way instead.
+
+        return result;
+    }
+
     /*!
     @brief inserts element
 
@@ -4949,9 +5015,7 @@ class basic_json
             }
 
             // insert to array and return iterator
-            iterator result(this);
+            return insert_iterator(pos, val);
-            result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, val);
-            return result;
         }
 
         JSON_THROW(type_error::create(309, "cannot use insert() with " + std::string(type_name())));
@@ -5002,9 +5066,7 @@ class basic_json
             }
 
             // insert to array and return iterator
-            iterator result(this);
+            return insert_iterator(pos, cnt, val);
-            result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, cnt, val);
-            return result;
         }
 
         JSON_THROW(type_error::create(309, "cannot use insert() with " + std::string(type_name())));
@@ -5066,12 +5128,7 @@ class basic_json
         }
 
         // insert to array and return iterator
-        iterator result(this);
+        return insert_iterator(pos, first.m_it.array_iterator, last.m_it.array_iterator);
-        result.m_it.array_iterator = m_value.array->insert(
-                                         pos.m_it.array_iterator,
-                                         first.m_it.array_iterator,
-                                         last.m_it.array_iterator);
-        return result;
     }
 
     /*!
@@ -5113,9 +5170,7 @@ class basic_json
         }
 
         // insert to array and return iterator
-        iterator result(this);
+        return insert_iterator(pos, ilist.begin(), ilist.end());
-        result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, ilist.begin(), ilist.end());
-        return result;
     }
 
     /*!
@@ -7663,19 +7718,6 @@ class basic_json
 // specialization of std::swap, and std::hash
 namespace std
 {
-/*!
-@brief exchanges the values of two JSON objects
-
-@since version 1.0.0
-*/
-template<>
-inline void swap<nlohmann::json>(nlohmann::json& j1, nlohmann::json& j2) noexcept(
-    is_nothrow_move_constructible<nlohmann::json>::value and
-    is_nothrow_move_assignable<nlohmann::json>::value
-)
-{
-    j1.swap(j2);
-}
 
 /// hash value for JSON objects
 template<>
@@ -7711,6 +7753,20 @@ struct less< ::nlohmann::detail::value_t>
     }
 };
 
+/*!
+@brief exchanges the values of two JSON objects
+
+@since version 1.0.0
+*/
+template<>
+inline void swap<nlohmann::json>(nlohmann::json& j1, nlohmann::json& j2) noexcept(
+    is_nothrow_move_constructible<nlohmann::json>::value and
+    is_nothrow_move_assignable<nlohmann::json>::value
+)
+{
+    j1.swap(j2);
+}
+
 } // namespace std
 
 /*!

meson.build

@@ -1,9 +1,13 @@
-project('nlohmann_json', 'cpp')
+project('nlohmann_json',
+    'cpp',
+    version : '3.2.0',
+    license : 'MIT',
+)
 
 nlohmann_json_dep = declare_dependency(
-  include_directories: include_directories('single_include')
+    include_directories: include_directories('single_include')
 )
 
 nlohmann_json_multiple_headers = declare_dependency(
-  include_directories: include_directories('include')
+    include_directories: include_directories('include')
 )

single_include/nlohmann/json.hpp

@@ -125,7 +125,7 @@ using json = basic_json<>;
             #error "unsupported Clang version - see https://github.com/nlohmann/json#supported-compilers"
         #endif
     #elif defined(__GNUC__) && !(defined(__ICC) || defined(__INTEL_COMPILER))
-        #if (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) < 40900
+        #if (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) < 40800
             #error "unsupported GCC version - see https://github.com/nlohmann/json#supported-compilers"
         #endif
     #endif
@@ -10149,7 +10149,7 @@ class serializer
             return;
         }
 
-        const bool is_negative = (x <= 0) and (x != 0);  // see issue #755
+        const bool is_negative = not (x >= 0);  // see issue #755
         std::size_t i = 0;
 
         while (x != 0)
@@ -13710,6 +13710,52 @@ class basic_json
         return JSONSerializer<ValueTypeCV>::from_json(*this);
     }
 
+    /*!
+    @brief get a value (explicit)
+
+    Explicit type conversion between the JSON value and a compatible value.
+    The value is filled into the input parameter by calling the @ref json_serializer<ValueType>
+    `from_json()` method.
+
+    The function is equivalent to executing
+    @code {.cpp}
+    ValueType v;
+    JSONSerializer<ValueType>::from_json(*this, v);
+    @endcode
+
+    This overloads is chosen if:
+    - @a ValueType is not @ref basic_json,
+    - @ref json_serializer<ValueType> has a `from_json()` method of the form
+      `void from_json(const basic_json&, ValueType&)`, and
+
+    @tparam ValueType the input parameter type.
+
+    @return the input parameter, allowing chaining calls.
+
+    @throw what @ref json_serializer<ValueType> `from_json()` method throws
+
+    @liveexample{The example below shows several conversions from JSON values
+    to other types. There a few things to note: (1) Floating-point numbers can
+    be converted to integers\, (2) A JSON array can be converted to a standard
+    `std::vector<short>`\, (3) A JSON object can be converted to C++
+    associative containers such as `std::unordered_map<std::string\,
+    json>`.,get_to}
+
+    @since version 3.3.0
+    */
+    template<typename ValueType,
+             detail::enable_if_t <
+                 not detail::is_basic_json<ValueType>::value and
+                 detail::has_from_json<basic_json_t, ValueType>::value,
+                 int> = 0>
+    ValueType & get_to(ValueType& v) const noexcept(noexcept(
+                JSONSerializer<ValueType>::from_json(std::declval<const basic_json_t&>(), v)))
+    {
+        JSONSerializer<ValueType>::from_json(*this, v);
+        return v;
+    }
+
+
     /*!
     @brief get a pointer value (implicit)
 
@@ -16002,6 +16048,26 @@ class basic_json
         return {it, res.second};
     }
 
+    /// Helper for insertion of an iterator
+    /// @note: This uses std::distance to support GCC 4.8,
+    ///        see https://github.com/nlohmann/json/pull/1257
+    template<typename... Args>
+    iterator insert_iterator(const_iterator pos, Args&& ... args)
+    {
+        iterator result(this);
+        assert(m_value.array != nullptr);
+
+        auto insert_pos = std::distance(m_value.array->begin(), pos.m_it.array_iterator);
+        m_value.array->insert(pos.m_it.array_iterator, std::forward<Args>(args)...);
+        result.m_it.array_iterator = m_value.array->begin() + insert_pos;
+
+        // This could have been written as:
+        // result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, cnt, val);
+        // but the return value of insert is missing in GCC 4.8, so it is written this way instead.
+
+        return result;
+    }
+
     /*!
     @brief inserts element
 
@@ -16036,9 +16102,7 @@ class basic_json
             }
 
             // insert to array and return iterator
-            iterator result(this);
+            return insert_iterator(pos, val);
-            result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, val);
-            return result;
         }
 
         JSON_THROW(type_error::create(309, "cannot use insert() with " + std::string(type_name())));
@@ -16089,9 +16153,7 @@ class basic_json
             }
 
             // insert to array and return iterator
-            iterator result(this);
+            return insert_iterator(pos, cnt, val);
-            result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, cnt, val);
-            return result;
         }
 
         JSON_THROW(type_error::create(309, "cannot use insert() with " + std::string(type_name())));
@@ -16153,12 +16215,7 @@ class basic_json
         }
 
         // insert to array and return iterator
-        iterator result(this);
+        return insert_iterator(pos, first.m_it.array_iterator, last.m_it.array_iterator);
-        result.m_it.array_iterator = m_value.array->insert(
-                                         pos.m_it.array_iterator,
-                                         first.m_it.array_iterator,
-                                         last.m_it.array_iterator);
-        return result;
     }
 
     /*!
@@ -16200,9 +16257,7 @@ class basic_json
         }
 
         // insert to array and return iterator
-        iterator result(this);
+        return insert_iterator(pos, ilist.begin(), ilist.end());
-        result.m_it.array_iterator = m_value.array->insert(pos.m_it.array_iterator, ilist.begin(), ilist.end());
-        return result;
     }
 
     /*!
@@ -18750,19 +18805,6 @@ class basic_json
 // specialization of std::swap, and std::hash
 namespace std
 {
-/*!
-@brief exchanges the values of two JSON objects
-
-@since version 1.0.0
-*/
-template<>
-inline void swap<nlohmann::json>(nlohmann::json& j1, nlohmann::json& j2) noexcept(
-    is_nothrow_move_constructible<nlohmann::json>::value and
-    is_nothrow_move_assignable<nlohmann::json>::value
-)
-{
-    j1.swap(j2);
-}
 
 /// hash value for JSON objects
 template<>
@@ -18798,6 +18840,20 @@ struct less< ::nlohmann::detail::value_t>
     }
 };
 
+/*!
+@brief exchanges the values of two JSON objects
+
+@since version 1.0.0
+*/
+template<>
+inline void swap<nlohmann::json>(nlohmann::json& j1, nlohmann::json& j2) noexcept(
+    is_nothrow_move_constructible<nlohmann::json>::value and
+    is_nothrow_move_assignable<nlohmann::json>::value
+)
+{
+    j1.swap(j2);
+}
+
 } // namespace std
 
 /*!

test/src/unit-json_patch.cpp

@@ -63,7 +63,7 @@ TEST_CASE("JSON patch")
             // is not an error, because "a" exists, and "b" will be added to
             // its value.
             CHECK_NOTHROW(doc1.patch(patch));
-            CHECK(doc1.patch(patch) == R"(
+            auto doc1_ans = R"(
                 {
                     "a": {
                         "foo": 1,
@@ -72,7 +72,8 @@ TEST_CASE("JSON patch")
                         }
                     }
                 }
-            )"_json);
+            )"_json;
+            CHECK(doc1.patch(patch) == doc1_ans);
 
             // It is an error in this document:
             json doc2 = R"({ "q": { "bar": 2 } })"_json;

test/src/unit-regression.cpp

@@ -1427,20 +1427,26 @@ TEST_CASE("regression tests")
             }
         })"_json;
 
-        CHECK_THROWS_AS(model.patch(R"([{"op": "move",
+        auto p1 = R"([{"op": "move",
-                         "from": "/one/two/three",
+                       "from": "/one/two/three",
-                         "path": "/a/b/c"}])"_json), json::out_of_range&);
+                       "path": "/a/b/c"}])"_json;
-        CHECK_THROWS_WITH(model.patch(R"([{"op": "move",
+        CHECK_THROWS_AS(model.patch(p1), json::out_of_range&);
-                         "from": "/one/two/three",
+
-                         "path": "/a/b/c"}])"_json),
+        auto p2 = R"([{"op": "move",
+                       "from": "/one/two/three",
+                       "path": "/a/b/c"}])"_json;
+        CHECK_THROWS_WITH(model.patch(p2),
                           "[json.exception.out_of_range.403] key 'a' not found");
 
-        CHECK_THROWS_AS(model.patch(R"([{"op": "copy",
+        auto p3 = R"([{"op": "copy",
+                       "from": "/one/two/three",
+                       "path": "/a/b/c"}])"_json;
+        CHECK_THROWS_AS(model.patch(p3), json::out_of_range&);
+
+        auto p4 = R"([{"op": "copy",
                                  "from": "/one/two/three",
-                                 "path": "/a/b/c"}])"_json), json::out_of_range&);
+                                 "path": "/a/b/c"}])"_json;
-        CHECK_THROWS_WITH(model.patch(R"([{"op": "copy",
+        CHECK_THROWS_WITH(model.patch(p4),
-                                 "from": "/one/two/three",
-                                 "path": "/a/b/c"}])"_json),
                           "[json.exception.out_of_range.403] key 'a' not found");
     }
 

test/src/unit-testsuites.cpp

@@ -405,7 +405,7 @@ TEST_CASE("RFC 7159 examples")
     SECTION("13 Examples")
     {
         {
-            CHECK_NOTHROW(json(R"(
+            auto json_contents = R"(
             {
                  "Image": {
                      "Width":  800,
@@ -420,11 +420,13 @@ TEST_CASE("RFC 7159 examples")
                      "IDs": [116, 943, 234, 38793]
                    }
                }
-            )"));
+            )";
+
+            CHECK_NOTHROW(json(json_contents));
         }
 
         {
-            CHECK_NOTHROW(json(R"(
+            auto json_contents = R"(
                 [
                     {
                        "precision": "zip",
@@ -446,7 +448,8 @@ TEST_CASE("RFC 7159 examples")
                        "Zip":       "94085",
                        "Country":   "US"
                     }
-            ])"));
+            ])";
+            CHECK_NOTHROW(json(json_contents));
         }
 
         CHECK(json::parse("\"Hello world!\"") == json("Hello world!"));
@@ -1343,13 +1346,11 @@ TEST_CASE("Big List of Naughty Strings")
     SECTION("roundtripping")
     {
         std::ifstream f("test/data/big-list-of-naughty-strings/blns.json");
+        std::string line;
 
-        while (not f.eof())
+        // read lines one by one, bail out on error or eof
+        while (getline(f, line))
         {
-            // read line
-            std::string line;
-            getline(f, line);
-
             // trim whitespace
             line = trim(line);
 

test/src/unit-udt.cpp

@@ -298,6 +298,19 @@ TEST_CASE("basic usage", "[udt]")
             CHECK(book == parsed_book);
         }
 
+        SECTION("via explicit calls to get_to")
+        {
+            udt::person person;
+            udt::name name;
+
+            json person_json = big_json["contacts"][0]["person"];
+            CHECK(person_json.get_to(person) == sfinae_addict);
+
+            // correct reference gets returned
+            person_json["name"].get_to(name).m_val = "new name";
+            CHECK(name.m_val == "new name");
+        }
+
         SECTION("implicit conversions")
         {
             const udt::contact_book parsed_book = big_json;