Re: [boost] Re: ScopeGuard

From: Peter Dimov (pdimov_at_[hidden])
Date: 2003-09-24 15:46:04

Daniel Wallin wrote:
>
> FWIW, here's the scopeguard implementation that I use:
>
>    namespace detail
>    {
>       class guard_base
>       {
>       public:
>          guard_base()
>             : m_dismissed(false)
>          {}
>
>          void dismiss() const
>          { m_dismissed = true; }
>
>       protected:
>          mutable bool m_dismissed;
>       };
>
>       template<class T>
>       class guard_impl : public guard_base
>       {
>       public:
>          explicit guard_impl(const T& x)
>             : m_action(x)
>          {}
>
>          ~guard_impl()
>          {
>             if (!m_dismissed)
>                m_action();
>          }
>
>       private:
>          T m_action;
>       };
>    }
>
>    template<class T>
>    detail::guard_impl<T> make_guard(T x)
>    {
>       return detail::guard_impl<T>(x);
>    }
>
>    typedef const detail::guard_base& scope_guard;

You are assuming that

    scope_guard g = make_guard(f);

will only create a single instance of guard_impl<F> (no copies), but this is
not guaranteed.