C++20 compatability -- std::result_of with std::invoke_result (#392)

* Replaced result_of with invoke_result_t.
* Fixed a few compile errors and updated CMakeLists.
* Updated Cloud CI

CMakeLists.txt

@@ -43,7 +43,7 @@ cmake_minimum_required(VERSION 3.2)
 
 project(g3log CXX)
 
-set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 if(NOT CMAKE_BUILD_TYPE AND NOT (MSVC_IDE OR XCODE))

appveyor.yml

@@ -2,7 +2,7 @@ environment:
   P: "c:/projects/libs"
 
 # Operating system (build VM template)
-os: Visual Studio 2015
+os: Visual Studio 2017
 
 # scripts that are called at very beginning, before repo cloning
 #init:
@@ -24,7 +24,7 @@ before_build:
   - cd build
 
 build_script:
-  - cmake -G "Visual Studio 14 2015 Win64" -DADD_G3LOG_UNIT_TEST=ON -DUSE_DYNAMIC_LOGGING_LEVELS=ON -DCHANGE_G3LOG_DEBUG_TO_DBUG=ON -DCMAKE_INSTALL_PREFIX=c:\g3log ..
+  - cmake -G "Visual Studio 15 2017 Win64" -DADD_G3LOG_UNIT_TEST=ON -DUSE_DYNAMIC_LOGGING_LEVELS=ON -DCHANGE_G3LOG_DEBUG_TO_DBUG=ON -DCMAKE_INSTALL_PREFIX=c:\g3log ..
   - cmake --build . --config Release --target install
 
 # scripts to run after build

scripts/.travis-bootstrap-ubuntu.sh

@@ -8,7 +8,7 @@ apt-get install -y apt-utils | true
 apt-get install -y software-properties-common | true
 apt-get install -y python-software-properties
 apt-get update -y
-add-apt-repository -y ppa:jonathonf/gcc-7.1
+add-apt-repository -y ppa:jonathonf/gcc
 apt-get update -y
 apt-get install -y cmake software-properties-common git make
 apt-get install -y gcc-7 g++-7

src/g3log/future.hpp

@@ -42,9 +42,9 @@ namespace g3 {
    //  auto msg_call=[=](){return ("Hello from the Background");};
    //  auto future_msg = g3::spawn_task(msg_lambda, bgWorker.get());
    template <typename Func, class BgWorker>
-   std::future<typename std::result_of<Func()>::type> spawn_task(Func func, BgWorker *worker)
+   std::future<std::invoke_result_t<Func>> spawn_task(Func func, BgWorker *worker)
    {
-      typedef typename std::result_of<Func()>::type result_type;
+      typedef std::invoke_result_t<Func> result_type;
       typedef std::packaged_task<result_type()> task_type;
 
       if (nullptr == worker) {

src/g3log/sink.hpp

@@ -70,7 +70,7 @@ namespace g3 {
          }
 
          template<typename Call, typename... Args>
-         auto async(Call call, Args &&... args)-> std::future< typename std::result_of<decltype(call)(T, Args...)>::type> {
+         auto async(Call call, Args &&... args)-> std::future<std::invoke_result_t<decltype(call), T, Args...>> {
             return g3::spawn_task(std::bind(call, _real_sink.get(), std::forward<Args>(args)...), _bg.get());
          }
       };

src/g3log/sinkhandle.hpp

@@ -37,12 +37,12 @@ namespace g3 {
       // the returned future will contain a bad_weak_ptr exception instead of the
       // call result.
       template<typename AsyncCall, typename... Args>
-      auto call(AsyncCall func , Args&& ... args) -> std::future<typename std::result_of<decltype(func)(T, Args...)>::type> {
+      auto call(AsyncCall func , Args&& ... args) -> std::future<std::invoke_result_t<decltype(func), T, Args...>> {
          try {
             std::shared_ptr<internal::Sink<T>> sink(_sink);
             return sink->async(func, std::forward<Args>(args)...);
          } catch (const std::bad_weak_ptr& e) {
-            typedef typename std::result_of<decltype(func)(T, Args...)>::type PromiseType;
+            typedef std::invoke_result_t<decltype(func), T, Args...> PromiseType;
             std::promise<PromiseType> promise;
             promise.set_exception(std::make_exception_ptr(e));
             return std::move(promise.get_future());

test_unit/test_cpp_future_concepts.cpp

@@ -75,9 +75,9 @@ TEST(TestOf_CopyableLambdaCall, Expecting_AllFine)
 
 
 template<typename F>
-std::future<typename std::result_of<F()>::type> ObsoleteSpawnTask(F f)
+std::future<std::invoke_result_t<F>> ObsoleteSpawnTask(F f)
 {
-  typedef typename std::result_of<F()>::type result_type;
+  typedef std::invoke_result_t<F> result_type;
   typedef std::packaged_task<result_type()> task_type;
 
   task_type task(std::move(f));
@@ -119,9 +119,9 @@ namespace WORKING
   std::vector<std::function<void()>> vec;
 
   template<typename F>
-  std::future<typename std::result_of<F()>::type> spawn_task(F f)
+  std::future<std::invoke_result_t<F>> spawn_task(F f)
   {
-    typedef typename std::result_of<F()>::type result_type;
+    typedef std::invoke_result_t<F> result_type;
     typedef std::packaged_task<result_type()> task_type;
 
     task_type task(std::move(f));

test_unit/testing_helpers.h

@@ -86,7 +86,7 @@ namespace testing_helpers {
 
 
       template<typename Call, typename ... Args >
-      typename std::result_of<Call(Args...)>::type callToLogger(Call call, Args&& ... args) {
+      std::invoke_result_t<Call(Args...)> callToLogger(Call call, Args&& ... args) {
          auto func = std::bind(call, _scope->get(), std::forward<Args>(args)...);
          return func();
       }