Re: [boost] lifetime of ranges vs. iterators

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2008-09-01 04:18:58

Giovanni Piero Deretta skrev:

>>> Stacking them naively would have 2^N storage
>>> growth, rather than 4^N, and we still don't need to worry about range
>>> lifetime.
>> I've been trying to say that generic algorithms *can't* worry about the
>> range lifetime; they have to assume that the iterators they're passed
>> will not be invalidated before they're destroyed.
> 
> I think that the OP is talking about a different problem: let say you
> want to name the result of stacked applications of range adaptors:
> 
> template<typename Range>
> void my_algo(Range& r) {
>   auto stacked_range = r | filtered(filter) | mapped(mapper);
>   // use stacked_range
> }
> 
> This may lead iterator lifetime problems, not because r iterators may
> be invalid, but because the iterators of the range returned by
> filtered(...) may become invalid as that temporary has been
> destructed. 

I don't see how this happens. The iterators are stored by value in each 
new range that is generated.

-Thorsten