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

Subject: Re: [boost] [range] [extensions] Default values for range access adaptors?
From: Akira Takahashi (faithandbrave_at_[hidden])
Date: 2013-06-05 09:09:09

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