Re: [Boost-users] Fwd: [bimap] Review of the Bimap library begins today Feb 15

From: Matias Capeletto (matias.capeletto_at_[hidden])
Date: 2007-02-19 12:05:20

On 2/19/07, Gottlob Frege <gottlobfrege_at_[hidden]> wrote:
> I was just concerned that you were putting too much meaning into
> std::pair (in general, not just in the context of maps).  The members
> never really should have been called 'first/second' (implying order or
> lack of symmetry or any other meaning).  I think it was just such a
> generic concept ('pair') that it was hard to name the members - maybe
> they should have just been called 'foo' and 'bar' to avoid any
> meaning.  So do you feel first/second has too much meaning, or that it
> has too much meaning and history in the context of map?  ie if you are
> saying that even if they were named foo/bar you would still want
> something different  so as to emphasize the difference from std::map,
> I can understand that.

As you said, first/second has a lot of meaning in the context of the
standard mapping framework. You have express it very clear.

> > > - I think 'relation' is too generic a word to abscond.
> >
> > >From the dictionary:
> > "A logical or natural association between two or more things"
>
> It is mostly the 'or more' that bothers me.  And that 'left/right' is
> more specific than 'relation'.  left <-> right is a very specific
> relation (called 'opposing directions' or something like that) as is
> first <-> second "before/after", as is "between" - a relation between
> 3 things.  'relation' is a term that covers all of these, and is thus
> too generic.  Do you want a term for a generic 2 item relation or a
> specific 2 item relation?  What are the properties of your specific
> relation? 'balanced'? 'invertable'?

'symmetric'...  'bidirectional'...
This discussion will surely take place later on the review.
If other people think that is better to rename this new beast, I have
no problem to change it.
The important thing is to maintain the left/right notation.

> In the end, it also hinges on the namespace issue.  'bimap::relation'
> is, to me, a very specific relation (the relation inherent in a
> bimap).  'boost::relation' or 'using bimap; ... relation' is polluting
> with a too generic term.

relation will be inside boost::bimap namespace, not in boost.

> > >    - the nature of typing code forces order - ie note that bimap<X, Y>
> > > is different than bimap<Y, X> (although philosophically the same).
> >
> > (Side Note: Using tags they are exactly the same.)

> The same to the compiler? and to boost::mpl? Cool.  And as it should be.

Yes, from the tutorial:

struct id   {}; // Tag for the identification number
struct name {}; // Tag for the name of the person

typedef bimap<
    tagged< int                , id   >,
    tagged< multiset_of<string>, name >
> People;

People people;
// ...
map_by<id>(people)[28928546] = "Gray Simpson";
map_by<name>(people).insert(
    value_type_by<name,People>("Marta Smith",30215692)
);
cout << get<id>(*people.begin());

You can write the instantiation as

typedef bimap<
    tagged< multiset_of<string>, name >,
    tagged< int                , id   >
> People;

and everything will just work.

Best Regards
Matias