Re: [boost] [proposal] Sequence container with O(log n)randomaccess _and_ O(log n) insertion/removal (wherever)

From: Martin Bonner (martin.bonner_at_[hidden])
Date: 2006-10-31 05:20:05

> On 10/30/06, Jason Hise <0xchaos_at_[hidden]> wrote:

>> Actually, I wonder if it is even valid to say
>> that this container supports random access... although it supports
>> the syntax for it, isn't random access defined as being constant
>> time? 
> 
From: Michael Fawcett
> I don't think so.  I'm pretty sure RandomAccess only means that the
> iterator supports the required arithmetic syntax, i.e. ++iter, iter++,
> iter + n, iter += n.  I am by no means an iterator guru.

Sorry.  Jason is right.  Section 24.1 paragraph 8 of the standard:
    All the categories of iterators require only those functions that 
    are realizable for a given category in constant time (amortized). 

(If there weren't a constant time requirement, there would be no point
in distinguishing bi-directional iterators from random access iterators.
bi-directional iterators can always implement += n by repeated
increment.)

-- 
Martin Bonner
Martin.Bonner_at_[hidden]
Pi Technology, Milton Hall, Ely Road, Milton, Cambridge, CB24 6WZ,
ENGLAND Tel: [phone]