Re: [lmi] Cating doubles to enums

[Vadim Zeitlin]

On Tue, 6 Nov 2018 00:36:17 +0000 Greg Chicares <address@hidden> wrote:

GC> For now, I've tried to cover all the floating-to-enum conversions
GC> so that an msvc build will work again. Let me commit that now and
GC> ask you to make sure that goal has been achieved.

 I can confirm that everything compiles fine with MSVS 2017 now, thank
you!

GC> Most of the changes are clearly for the better IMO, but this one
GC> bothers me:
GC> 
GC> -    oenum_alb_or_anb const alb_anb =
GC> -        static_cast<oenum_alb_or_anb>
GC> -            (database_->Query(DB_AgeLastOrNearest)
GC> -            );
GC> +    oenum_alb_or_anb alb_anb;
GC> +    database_->query_into(alb_anb, DB_AgeLastOrNearest);
GC> 
GC> because there's no 'alb_anb' data member to assign into;

 Sorry but why is this a problem? I.e. why should query_into() be only used
with members and not local variables?

GC> maybe
GC> that suggests that such a member should exist, or maybe it means
GC> I should reverse the order of the function template arguments
GC> and default the "destination" argument:
GC> 
GC>  template<typename T>
GC> -void product_database::query_into(T& dst, e_database_key k) const
GC> +T product_database::query_into(e_database_key k, T& dst = T(0)) const

 This won't compile, will it? A non-const reference can't be bound to a
temporary.

GC> to allow some syntax like
GC> 
GC> -    oenum_alb_or_anb alb_anb;
GC> -    database_->query_into(alb_anb, DB_AgeLastOrNearest);
GC> +    auto const alb_anb = 
{database_->query_into<oenum_alb_or_anb>(DB_AgeLastOrNearest)};

 It looks like you're really looking for what had been suggested before,
i.e.

        template<typename T>
        T product_database::query_into(e_database_key k) const;

which could then be used as

        auto const alb_anb = query_into<oenum_alb_or_anb>(DB_AgeLastOrNearest);

 Or am I missing something?
VZ