[boost] Re: Re: Re: relational table as an STL container --anyinterest?

From: Arkadiy Vertleyb (vertleyb_at_[hidden])
Date: 2002-11-04 13:46:43

Can't we achieve the same result with:

c1* field_c1 = 0;
tuple[field_c1] = 5;

?

Arkadiy

"Joel de Guzman" <djowel_at_[hidden]> wrote in message
news:003101c2841b$f916a730$4f4ca7cb_at_kim...
>
> ----- Original Message -----
> From: "James Curran/MVP" <jamescurran_at_[hidden]>
>
> > Shouldn't this work?
> >
> > template <typename fld>
> > fld& Field(Tuple& tuple)
> > {
> >      return tuple.field((fld*)0);
> > }
> >
> >  Field<c1>(tuple) = 5;
>
> or how about:
>
>     tuple[field<c1>()] = 5;
>
> where field:
>
>     template <ColumnT>
>     struct field { /*...*/ };
>
> The user, may even declare:
>
>     field<c1> const field_c1 = field<c1>();
>
> Then:
>
>     tuple[field_c1] = 5;
>
> --Joel
>
>
> > Truth,
> > James Curran
> > www.NovelTheory.com  (Personal)
> > www.NJTheater.com   (Professional)
> > www.aurora-inc.com   (Day job)
> >
> >
> > "Arkadiy Vertleyb" <vertleyb_at_[hidden]> wrote in message
> > news:apv09f$1eq$1_at_main.gmane.org...
> > > I like this "when" that you use instead of "if" :o))
> > >
> > > We have two basic macros: COLUMN and FIELD.
> > >
> > > I don't think COLUMN can be eleminated.  What it does -- it defines a
> > class
> > > a1 that holds an integer value.  This class is derived from
> > rel::column<int>
> > > (we can't use rel::column<int> directly, because then there would be
> > nothing
> > > that distinguish one int colomn from another).  The reason we need
> > macro --
> > > we need to define a constructor from int, that just forwards to
> > > rel::column<int> constructor...
> > >
> > > The FIELD macro is used to access a field inside a tuple.  It unwraps
into
> > > the call to the templated method on the tuple class that further calls
> > > static_cast to access the field.  So we now have:
> > >
> > > FIELD(tuple, c1) = 5; // we have it now
> > >
> > > but would like to have:
> > >
> > > tuple.field<c1>() = 5; // we want it like this
> > >
> > > Neither MSVC nor g++ allows us to do this.  Is there anything about
the
> > > standard that makes it illigal?  The best we could do is:
> > >
> > > tuple.field((c1*)0) = 5; // pretty ugly, isn't it?
> > >
> > > So, we decided to have the macro :o((
> > >
> > > One way to deal with this is to use COLUMN macro to reduce the need in
the
> > > FIELD macro.  In addition to the above mentioned constructor, it could
> > > define, say, getter and setter, so we could do the following:
> > >
> > > tuple.set_c1(5); // better.
> > > // tuple.c1() = 5 would be even better, but this name is reserved for
the
> > > constructor
> > >
> > > Unfortunately not all the columns are defined by the COLUMN macro.
Some,
> > > like renamed fields, are generated automatically, and can't use the
latter
> > > approach.
> > >
> > > Any suggestions about this (or anything else) are most welcome.
> > >
> > > Arkadiy
> > >
> > > "Joel de Guzman" <djowel_at_[hidden]> wrote in message
> > > news:00b701c281eb$bcc15640$0100a8c0_at_kim...
> > > > Just a quick question: Can you eliminate the ugly MACRO?
> > > > When the library ever gets into boost, that would have to be
> > > > renamed to something like:
> > > >
> > > >     BOOST_LIBRARY_NAME_COLUMN(a1, int)
> > > >
> > > > Yuck!
> > > >
> > > > --Joel
> > > >
> > > > ----- Original Message -----
> > > > From: "Arkadiy Vertleyb" <vertleyb_at_[hidden]>
> > > >
> > > > > 1. We can have a column whose type is a table (see code below);
> > > > > 2. As far as other relations (operators) are concerned, right now
we
> > > can't
> > > > > do this because currently the operators are not default
constructible.
> > > This
> > > > > could be easily fixed.
> > > > > 3. Just out of curiosity, how would you use this feature?  It
might
> > > become a
> > > > > major advantage of this library over traditional RDBMSs.
> > > > >
> > > > > Arkadiy
> > > > >
> > > > > ==============================
> > > > >
> > > > > COLUMN(a1, int);
> > > > > typedef tuple<list<a1> > tuplea_type;
> > > > > typedef table<tuplea_type> tablea_type;
> > > > >
> > > > > COLUMN(b1, int);
> > > > > COLUMN(b2, tablea_type);
> > > > > typedef tuple<list<b1, list<b2> > > tupleb_type;
> > > > > typedef table<tupleb_type, list<b1> > tableb_type;
> > > > >
> > > > > void foo() {
> > > > >   tableb_type tab;
> > > > >   for (int i = 0; i < 5; ++i) {
> > > > >     tablea_type t;
> > > > >     t.insert(i);
> > > > >     t.insert(i * i);
> > > > >     t.insert(i * i * i);
> > > > >     tab.insert(tupleb_type(i, t));
> > > > >   }
> > > > >   for (tableb_type::const_iterator it = tab.begin(); it !=
tab.end();
> > > ++it){
> > > > >     cout << "tuple " << FIELD(*it, b1) << endl;
> > > > >     print(FIELD(*it, b2));
> > > > >   }
> > > > > }
> > > >
> > > >
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