[Boost-users] any boost library for referring a portion of the container ?

From: abir basak (abirbasak_at_[hidden])
Date: 2007-02-16 02:36:39

Hi,
   I am having a few containers whose some portion I want to refer to 
another class (sometime I need to refer to a continuous portion, while 
sometime need a non-continuous portion) .
   At present I have written all of these myself. But wondering if a few 
portion can be substituted by some boost library.

Just to make the concept clear, I am elaborating the structure and why 
it is done in that way.
In the program it takes the user handwriting (as entered using digital 
pen etc) and analysis them.
as user writes, I register points (x,y coord) and put them in an deque 
(in actual case I am using boost::circular_buffer_space_optimized ).

Now, a second deque (or other container) stores another structure Trace, 
which has 2 index pointing start & end of that continuous writing until 
pen up occurs. These have to be 2 index rather than iterator, as 
iterator may get (and usually gets ) invalidated while more points are 
added in the point deque.  Thus Trace refers deque<Point>
Now from the trace structure I return the points for the trace 
(boost::sub_range ) using the 2 index and the deque (i.e from 
deque<Point> get iterator, add index as offset , make sub_range and 
return).
Now these are the continues portions , referred by 2 index.
Next, some such things can be even not continuous. In that case I store 
all index to which it points (in a vector ) and return a sub_range kind 
of structure (named index_range ) which takes these index and a 
container, and iterates over it jumping by those specific offsets.

Example can be a Character class which refers some of those traces , not 
necessarily continuous (like user writes a dot much later than the i , 
thus Character i contains index of the vertical stroke of the i & dot )

Similarly more hierarchy are constructed, like Trace => Page, and 
Character => Word => Line => Paragraph => Page etc.

Most of them contains 2 index and with the help of the container returns 
  a boost sub_range , while some contains a vector of index (size_t) and 
returns index_range (created by me) .

So far I found it is the ONLY way to create a level of hierarchy/ view 
from different set of dynamic data. (The other can be storing everything 
  as a pointer in the container, and creating by new, in that case no 
problem arises as the objects are not movable, but in C++ it is quite 
bad solution)

A Graphical representation is like,
=============== deque<Point> =====================
<=remove old data             => add new data
|  1 |  2   | 3    | 4   | 5   | 6   | 7  | 8   |
=============== deque<Trace> ====================
|    1                    |          2          |
=============== deque<Page> =====================

These are for continuous data (i.e 2 index struct & boost::sub_range )

================ deque<Trace> ====================
|1,3,4|  2 | 5,6 | 7,9 | 8 | ...
================== deque<Character> ===============
| 1,2,4, 5 | 3 | ....
================== deque<Word> =====================
| 1 | 2 | 3 | .... (assuming past a line user doesn't correct word, they 
can be made a pair of index ! )
================== deque<Line> =====================
....
================== deque<Paragraph> ================ etc...

  My question ,
1) had anyone faced these kind of design , where a class referrers a 
portion of STL container ? and multiple view from same set of data 
exists (otherwise I could had Trace contains the points , instead of 
having index of the portion, if Trace is the only view for the points )

2) Any boost library / other library is there to help these kind of 
design ?

I had posted a same kind of topic in C++ newsgroup also, but it seems 
their people are more concerned with answering C++ standard based 
question . I think, boost may be the better news group to ask this 
question, as boosters work in a broader area.

Thanks to all, esp to those who share their thought on it ...
abir

-- 
Abir Basak, Member IEEE
B. Tech, IIT Kharagpur
email: abir_at_[hidden]
homepage: www.abirbasak.com