Re: [boost] [range] [extensions] Default values for range access adaptors?

Subject: Re: [boost] [range] [extensions] Default values for range access adaptors?
From: Viktor Sehr (viktor.sehr_at_[hidden])
Date: 2013-06-05 11:02:23

Hi,
I totally agree, returning a boost::optional is a better solution than what
I proposed. Is there any way around this right now, or does the range
accessors require a non-empty range not to result in undefined
behavior\crash?

I'm very much looking forward to having range extensions included in boost.
/Viktor

On Wed, Jun 5, 2013 at 3:09 PM, Akira Takahashi <faithandbrave_at_[hidden]>wrote:

> Hi  Viktor,
>
> 2013/6/5 Viktor Sehr <viktor.sehr_at_[hidden]>
>
> > I'd like to suggest the addition of a default value to the range access
> > adaptors. Either by adding it as an extra, non-necessary parameter for
> the
> > functions, or by duplicating the functions as "front_or_default(T default
> > value)".
> >
> > For example it would be useful for finding objects which I am not sure
> > exists in a range.
> >
> > std::vector<int> vec = boost::assign::list_of(2)(4)(6);
> > auto first_odd = vec | filtered(is_odd) | front(); // undefined?
> > auto first_odd = vec | filtered(is_odd) | front_or_default(-1);  //
> > everything is fine!
> >
> > Another option would be a function which returns the adress, or nullptr
> if
> > the value does not exist?
> >
> > /Viktor
> >
>
> My Boost.Range Extension has `front` accessor.
>
>
> http://dl.dropboxusercontent.com/u/1682460/git/OvenToBoost/libs/range/doc/html/range_extension/reference/range_access.html
> https://github.com/faithandbrave/OvenToBoost/tree/master/boost/range/access
>
> This is now proposing to Boost.Range.
>
> However, I don't have `front_or_default` feature.
> I think better way is add `optional_front` feature (return
> boost::optional<T&>). Because `front` return `T&` but default value is not
> reference.
>
> Thanks,
> Akira
>
> >>========================
> Akira Takahashi
> mailto:faithandbrave_at_[hidden]
> https://sites.google.com/site/faithandbrave/about/en
>
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