WinSTL Registry library mods and fixes, part 3: exception-safety

In reviewing the implementation of the WinSTL Registry Library's winstl::basic_reg_value class - as described in part 1 and part 2 of this series of posts - I've also spotted a defect in exception-safety.

Consider the (chopped-down) definition of the basic_reg_value class:

template < . . . >
class basic_reg_value
{
. . .
private:
hkey_type    m_hkey; // The parent key of the value
string_type  m_name; // The name of the value
. . . // other members
};

The m_hkey member is obtained via winstl::reg_traits<>::reg_dup_key(). It is the basic_reg_value class itself that provides the RAII. Consequently, if any exception occur during its constructor, the release of m_hkey will not be carried out.

Since the m_name is a string class instance, its constructor can throw. Consequently, basic_reg_value is not exception safe.

Thankfully, the fix is very simple. Simply reverse the order of declaration of the two members. If m_name's constructor throws, that'll happen before the key duplication takes place. If the key duplication throws an exception, the (fully constructed) m_name's destructor will be invoked. Q.E.D.