[C++-sig] Re: Support for Indexing and Iteration Safety

[David Abrahams]

"Brett Calcott" <brett.calcott at paradise.net.nz> writes:

<snip my entire posting quoted>

> I'm haven't gone far enough in what I am doing to encounter these
> problems, but for what its worth, at the moment I would have done the
> following:
>
>     if something is lightweight, return a copy
>     if it is big, use shared_ptr
>
> Which means that the above problems 3 & 4 would not occur. 

That is only true if you can modify your vector to be a
vector<shared_ptr<SomeBigObject> >.  Often, the implementation of code
being wrapped can't be intrusively changed in that way.  Furthermore,
even if it's lightweight, returning a copy gets you unpredictable
behavior like:

      >>> v[3].foo = 1
      >>> v[3].foo
      22

because you've only set the attribute on the copy.

> And 1 & 2 don't really seem that onerous a task. So I guess I don't
> 'care' that much.

Hmm, this might be a case of "those sophisticated enough to know what
I'm talking about also know how to avoid the problems."

Where are all the other respondents?  I know a number of people have
tried to wrap things with array indexing in the past...

http://aspn.activestate.com/ASPN/Mail/Message/1428806
http://aspn.activestate.com/ASPN/Mail/Message/1465837
http://aspn.activestate.com/ASPN/Mail/Message/1227141
http://aspn.activestate.com/ASPN/Mail/Message/1227504
http://aspn.activestate.com/ASPN/Mail/Message/1431504
http://aspn.activestate.com/ASPN/Mail/Message/1425273
http://aspn.activestate.com/ASPN/Mail/Message/1227378

> Of course, I reserve the right to change my opinion at any moment if I
> encounter problems :)

Did I change your mind yet? ;->

<snip a duplicate copy of the entire foregoing text>


-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com