Merge branch 'develop' into feature/manual_lexer

.travis.yml

@@ -207,6 +207,27 @@ matrix:
     env: LLVM_VERSION=3.8.1
     compiler: clang
 
+#  - os: linux
+#    addons:
+#      apt:
+#        sources: llvm-toolchain-trusty-3.9
+#        packages: clang-3.9
+#    env: COMPILER=clang++-3.9
+#
+#  - os: linux
+#    addons:
+#      apt:
+#        sources: llvm-toolchain-trusty-4.0
+#        packages: clang-4.0
+#    env: COMPILER=clang++-4.0
+#
+#  - os: linux
+#    addons:
+#      apt:
+#        sources: llvm-toolchain-trusty
+#        packages: clang-5.0
+#    env: COMPILER=clang++-5.0
+
 #####################
 # installation step #
 #####################

README.md

@@ -841,7 +841,7 @@ Thanks a lot for helping out! Please [let me know](mailto:mail@nlohmann.me) if I
 
 ## Used third-party tools
 
-The library itself contains of a single header file licensed under the MIT license. However, it is built, tested, documented, and whatnot using a lot of thirs-party tools and services. Thanks a lot!
+The library itself contains of a single header file licensed under the MIT license. However, it is built, tested, documented, and whatnot using a lot of third-party tools and services. Thanks a lot!
 
 - [**American fuzzy lop**](http://lcamtuf.coredump.cx/afl/) for fuzz testing
 - [**AppVeyor**](https://www.appveyor.com) for [continuous integration](https://ci.appveyor.com/project/nlohmann/json) on Windows

appveyor.yml

@@ -1,12 +1,27 @@
 version: '{build}'
+
 os: 
   - Visual Studio 2015
   - Visual Studio 2017
+
+environment:
+  matrix:
+  - additional_flags: ""
+  - additional_flags: "/permissive- /std:c++latest /utf-8"
+
+matrix:
+  exclude:
+    - additional_flags: "/permissive- /std:c++latest /utf-8"
+      os: Visual Studio 2015
+  
 init: []
+
 install: []
+
 build_script:
   - IF "%APPVEYOR_BUILD_WORKER_IMAGE%" == "Visual Studio 2015" ( SET GEN="Visual Studio 14 2015") ELSE (SET GEN="Visual Studio 15 2017")
-- cmake . -G%GEN% 
+  - cmake . -G%GEN% -DCMAKE_CXX_FLAGS="%additional_flags%"
   - cmake --build . --config Release
+
 test_script:
   - ctest -C Release -V

src/json.hpp

@@ -3739,6 +3739,9 @@ class basic_json
                    not std::is_same<ValueType, typename string_t::value_type>::value
 #ifndef _MSC_VER  // fix for issue #167 operator<< ambiguity under VS2015
                    and not std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value
+#endif
+#if defined(_MSC_VER) && defined(_HAS_CXX17) && _HAS_CXX17 == 1 // fix for issue #464
+                   and not std::is_same<ValueType, typename std::string_view>::value
 #endif
                    , int >::type = 0 >
     operator ValueType() const