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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.

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


Akira Takahashi

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