template< class ErrorCodeEnum >
error_code& operator=( ErrorCodeEnum e ) noexcept;

error_code& operator=( const error_code& other ) = default;

error_code& operator=( error_code&& other ) = default;

1) Replaces the error code and corresponding category with those representing error code enum e.
Equivalent to *this = make_error_code(e), where make_error_code is only found by argument-dependent lookup. This overload participates in overload resolution only if std::is_error_code_enum<ErrorCodeEnum>::value is true.

2,3) Implicitly defined copy-assignment operator and move-assignment operator assign the contents of other to *this.