[boost] Re: circular_buffer question

From: Pavel Vozenilek (pavel_vozenilek_at_[hidden])
Date: 2004-04-13 05:23:14

"Jan Gaspar" <jano_gaspar_at_[hidden]> wrote

(snip using negative values for index in operator[] )

There are few different cases:

1. operator[] for circular_buffer iterator:

   circular_buffer<int> b(10);
   ... fill buffer
   circular_buffer<int>::iterator it = b.begin() + 5;
   int x = it[-1]; // should return value b[4]

I think here negative values should be allowed here
(provided they result in valid offset).

2. operator[] for circular_buffer itself:

   circular_buffer<int> b(10);
   b.push_back(10);
   b.push_back(20);
   b.push_back(33);
   int x = b[-1];  // this would return value 30, the last one
   x = b[-2]; // would return 20

This would be new feature, not available in current
standard ontainers. I remember some language
(forgot name) provides it.

I personally would like to have this feature
and have it in std::vector/deque too.

Alternatively one can think about syntax as:
int x = b[boost::end - 1];
to indicate intent and catch possible bugs.

(boost::end would be tag type and operator[]
would be overloaded.)

3. incrementing/decrementing circular_buffer
    iterator with automatic wrap-around:

    I think this (wrap-around) should not be
    allowed:
    - it could hide errors
    - it suggests circular-linked-list semantics
      (and one can then ask for rotate())

/Pavel