[Kim-J-Smith]

1. Remove unnecessary protected: in member_variable_impl.
2. Add more assertions in exception tests.

[Kim-J-Smith]

#6 [2/3] RUN wget -q "https://cmake.org/files/v3.15/cmake-3.15.7-Linux-x86_64.tar.gz"     -O /tmp/cmake.tar.gz     && tar -xzf /tmp/cmake.tar.gz -C /usr/local --strip-components=1     && rm -f /tmp/cmake.tar.gz
#6 ERROR: process "/bin/sh -c wget -q \"[https://cmake.org/files/v3.15/cmake-${CMAKE_VERSION}-Linux-x86_64.tar.gz\](https://cmake.org/files/v3.15/cmake-$%7BCMAKE_VERSION%7D-Linux-x86_64.tar.gz/)"     -O /tmp/cmake.tar.gz     && tar -xzf /tmp/cmake.tar.gz -C /usr/local --strip-components=1     && rm -f /tmp/cmake.tar.gz" did not complete successfully: exit code: 4
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 > [2/3] RUN wget -q "https://cmake.org/files/v3.15/cmake-3.15.7-Linux-x86_64.tar.gz"     -O /tmp/cmake.tar.gz     && tar -xzf /tmp/cmake.tar.gz -C /usr/local --strip-components=1     && rm -f /tmp/cmake.tar.gz:
------
Dockerfile:6
--------------------
   5 |     
   6 | >>> RUN wget -q "[https://cmake.org/files/v3.15/cmake-${CMAKE_VERSION}-Linux-x86_64.tar.gz](https://cmake.org/files/v3.15/cmake-$%7BCMAKE_VERSION%7D-Linux-x86_64.tar.gz)" \
   7 | >>>     -O /tmp/cmake.tar.gz \
   8 | >>>     && tar -xzf /tmp/cmake.tar.gz -C /usr/local --strip-components=1 \
   9 | >>>     && rm -f /tmp/cmake.tar.gz
  10 |     
--------------------
ERROR: failed to build: failed to solve: process "/bin/sh -c wget -q \"[https://cmake.org/files/v3.15/cmake-${CMAKE_VERSION}-Linux-x86_64.tar.gz\](https://cmake.org/files/v3.15/cmake-$%7BCMAKE_VERSION%7D-Linux-x86_64.tar.gz/)"     -O /tmp/cmake.tar.gz     && tar -xzf /tmp/cmake.tar.gz -C /usr/local --strip-components=1     && rm -f /tmp/cmake.tar.gz" did not complete successfully: exit code: 4
Error: Process completed with exit code 1.

[Kim-J-Smith]

Re-run GCC 5 CI.