Why doesn't this enum convert to int?

Question

Why does the following code not compile under g++ (C++14), MSVC (C++14), or ARM (C++03)?

The named Error instance calls the integer constructor, but the anonymous Er

Answer 1

main.cpp:19:18: error: no matching function for call to 'Error::Error()'
Error(value_1);

The compiler tries to call the non-existent default constructor Error::Error() because it sees

Error(value_1);

as a variable declaration

Error  value_1;

A declaration is allowed to have redundant parenthesis.