feat: finally prepared for c++20 or c++17

.bazelrc

@@ -1,4 +1,4 @@
-build --cxxopt='-std=c++20'
+build --cxxopt='-std=c++17'
 build --cxxopt='-Wno-macro-redefined'
 build --cxxopt='-Wno-builtin-macro-redefined'
 #### https://github.com/llvm/llvm-project/issues/56709

README.md

@@ -28,6 +28,8 @@ If you want to help, please see instructions on [Development.md](./Development.m
 
 ### Advice for online environments
 
+OptFrame now supports both `c++17` and `c++20`.
+
 Before installing optframe online (such as google colab), check C++ compiler (typically GCC) version:
 
 `x86_64-linux-gnu-gcc -v`

docs/source/install.rst

@@ -14,7 +14,7 @@ Installing `optframe` package in Python is quite easy with pip.
    python -m pip install optframe
 
 .. warning::
-    The standard configuration will require a modern c++ compiler with C++20 support.
+    The standard configuration will require a modern c++ compiler with C++17 support, or maybe C++20.
     Note that, by 2022, this is already standard on recent MacOS software and Ubuntu 22.04 (g++ v11 is recommended... g++ v9 will not work!).
     On Windows/WSL environment, it is possible to upgrade WSL and g++. 
     Native Windows C++ compiler has not been tested yet... please try WSL first.

setup.py

@@ -43,7 +43,7 @@ def run(self):
         # git fetch
         # git checkout origin/master -ft
         subprocess.check_call(
-            ['git', 'clone', '--depth', '1', '--branch', '5.0.14', 'https://github.com/optframe/optframe', 'optframe-git'])
+            ['git', 'clone', '--depth', '1', '--branch', '5.0.15', 'https://github.com/optframe/optframe', 'optframe-git'])
         # ===== check that clone() was done fine ======
         # subprocess.check_call(
         #    ['ls', '-la', 'optframe-git'])
@@ -94,12 +94,8 @@ def get_ext_filename(self, ext_name):
                 this_directory, "./optframe-git/include")],
             #
             # ====================================================
-            # TODO: we should start using c++20 ASAP...
-            # Are Ubuntu / Windows / WSL2 users ready?
-            #
-            extra_compile_args=['--std=c++20']
-            # IF ONLY C++17 IS SUPPORTED, ON GCC, USE THIS (WE NEED CONCEPTS):
-            # extra_compile_args=['--std=c++17', '-fconcepts']
+            # In the future, try c++20. For now, too early.
+            extra_compile_args=['--std=c++17']
         ),
     ],
     # package_data includes data from 'src/' folder, by default