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Subject: Re: [boost] Proposed interface change to boost::algorithm::copy_while
From: Sebastian Redl (sebastian.redl_at_[hidden])
Date: 2013-02-20 15:26:12

On 20.02.2013, at 19:55, Marshall Clow wrote:

> I'm proposing to change the interface to:
> template<typename InputIterator, typename OutputIterator, typename Predicate>
> std::pair<InputIterator, OutputIterator>
> copy_while ( InputIterator first, InputIterator last, OutputIterator result, Predicate p );
> i.e, changing the return type to return both iterators.
> What this means:
> * If you're not calling copy_while (or copy_until), then this change won't affect you.
> * If you're not using the return value, then this change won't affect you.
> * If you are using the return value, then you will have to change your code thus:
> Old foo = copy_while ( first, last, out, p );
> New: foo = copy_while ( first, last, out, p ).second;

If you want to ease transition, I once wrote a biased_pair type, which is basically a pair with an implicit conversion to one of its member types.

template <typename T1, typename T2>
struct right_biased_pair { // consider deriving from std::pair instead of aping it
  T1 first;
  T2 second;

  // constructors and stuff

  operator std::pair<T1, T2>() { return std::pair<T1, T2>(first, second); }

  // the bias
  operator T2() const { return second; }

Then you can make copy_while return a right_biased_pair<InputIterator, OutputIterator> and code of the form
out = copy_while(first, last, out, p);
will keep working.

No idea if that's worth it to you, just saying that the option is there.


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