[Boost-users] [proto] iterating array expressions

Subject: [Boost-users] [proto] iterating array expressions
From: Daniel Oberhoff (daniel.oberhoff_at_[hidden])
Date: 2009-01-11 16:21:26

Hi,

First off: much thanks for previous replies to related problems. One  
comment: I got told to properly use proto on my array class I needed  
to separate data from user interface. I found now that it is possible  
to define expressions non-intrusively without having to change my  
array structure, but still I understand the motivation, and possibly  
this way is better anyway.

Anhow, now to my new problems. I have now set up proto to be able to  
evaluate expressions such as:

A(_i,_j) + B(_j,_i*_j-2)

at a given index (i.e. substituting given numbers for index  
placeholders _i and _j).

Here A and B are of my own n-dimensional array class.

Now I would like to iterate such expressions efficiently to evaluate  
assignment expressions like:

C = A(_i,_j) + B(_j,_i*_j-2);

efficiently.

What I want to do is base it around basic "iterators" for each array  
indexing expression ( i.e. B(_j,_i*_j-2) and A(_i,_j) in the example)  
that know how to move to a certain setting for the index placeholders  
and how to advance along the index placeholders (e.g. advance the data  
pointer for _i -> _i+1, _j -> _j+1). I think I could implement such  
iterators (not in the STL sense, since I dont use begin/end, but  
enough for what I need) for the array indexing expressions, but I dont  
know how to generate the iterator for the complete expression. I would  
like such an iterator be generated automatically given the individual  
iterators for the array indexing expressions and be able to call move,  
advance, and evaluate on such an iterator.

Any hints on where to start before I lose myself deeply in the  
documents and examples?

Any help much appreciated.

Best

Daniel