Re: [boost] Scoped Enum Emulation

Subject: Re: [boost] Scoped Enum Emulation
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2012-01-26 14:34:48

Vicente J. Botet wrote:
> Le 26/01/12 14:56, Stewart, Robert a écrit :
>
> >>       inline NT(enum_type v) : v_(v) {} \
> >>       inline underlying_type underlying() const {return
> v_;} \
> >
> > I've always preferred naming such functions with an "as_"
> > prefix.  In this context, you actually know the name of the
> > underlying type, so you could even do as_##UT, though that
> > wouldn't work right for unsigned int, signed int, etc.  Maybe
> > the preprocessor can help, for example, to collapse "unsigned
> > int" to "unsigned" so you could generate "as_unsigned" even
> > when UT is "unsigned int".
>
> I have no used underlying yet. It was just there to show a
> workaround when there is no explicit conversion. Anyway to make
> the user code portable, he can not use the member function as
> enum class don't have it. That mean s that we need a non-member
> function, let me call it underlying_cast,
>
> namespace boost
> {
> #ifdef BOOST_NO_SCOPED_ENUMS
>    template <typename UT, typename NT>
>    UT underlying_cast(NT v)
>    {
>      return v.underlying();
>    }
> #else  // BOOST_NO_SCOPED_ENUMS
>    template <typename UT, typename NT>
>    UT underlying_cast(NT v)
>    {
>      return static_cast<UT>(v);
>    }
> #endif
> }
>
> The portable explicit conversion to the underlying type
> becomes
>
>    int i = boost::underlying_cast<int>(e);

That is better.  The existence of underlying() is, then, an implementation detail.  Indeed, you might name it something more ominous: "detail_as_underlying", perhaps.

> At the end I'm wondering if the implicit conversion should
> even be provided

Without it, static_cast<underlying_type>(e) won't work, but that's valid for the real thing.

> I will commit something on the sandbox soon so that we can
> continue improving it.

OK

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer                     using std::disclaimer;
Dev Tools & Components
Susquehanna International Group, LLP  http://www.sig.com

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