Re: [boost] Boost.Bimap - first/second and left/right

From: Fernando Cacciola (fernando_cacciola_at_[hidden])
Date: 2007-03-05 11:53:36

Matias Capeletto wrote:
> Hi all,
>
> I think we must discuss this issue together so we can settled it down.
>
> Lets analyze the rationale step by step.
>
> (1) Interface for the bidirectional mapping. That interface have to be
> compatible with existing code that work with standard maps. The best
> way IMHO to achieve this is that you can view the container from the
> two sides and see something compatible with std::map<X,Y> for the left
> one and with std::map<Y,X> for the right one.
>
> (2) This force us to use first/second notation for the left view
> (first is the left element and second the right one) and for the right
> view (where the names are inverted, first is the right element and
> second is the left one)
>
I found the phrase "first/second notation" a bit confusing. Mainly becasuse 
is easy to mixup the notation for each view with the notation for each 
element in the view's value_type.
You can refer to is as: "a std::pair-compatible struct is used as the value 
type of the left/right views".

> (3) (from other thread) For bm (the above view)

As I said in another post, considering the set of relation objects as a view 
"from above" is a valid but nevertheless arbitrary POV.
You can of course choose to see it like that, but make sure not to present 
it as a natural choice.
Ultimately, you don't actually need to think of it as being above, or over, 
or along, or whatever...

> a) bm can be left without any special function and so force the user
> to write .left or .right to refer to it.
> b) bm can be the same as bm.left. This IMHO introduce an asymmetry to
> the interface. The left view became the more important than the right
> view.
> c) bm can be used for something new. Give the user a new view of the
> mapping: a set of relations.

Right, and as others said I'd call it ".relations".
Definitely not ".above".

> The library use (c) because it is very useful to be able to insert the
> elements or ask for the size, etc directly. And because it allows us
> to extend the framework by selecting different set of relations.

> So first/second are used in the side views

More precisely, to name the elements of the value_type of the side views.

>and left/right in the above view.

Again, more precisely, to name the elements of the value_type of the above 
view.

Being more precise is important in your context because you not only have 
left/right elements but also left/right views.
Sometimes the right overload is a bit hard to pick up.

Best

-- 
------
Fernando Cacciola
SciSoft
http://certuscode.wordpress.com
http://fcacciola.50webs.com
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