[Boost-users] range: partition a transformed range adaptor

Subject: [Boost-users] range: partition a transformed range adaptor
From: Auer, Jens (jens.auer_at_[hidden])
Date: 2015-10-02 06:18:02

Hi,

So today I wanted to partition a transformed range. I came up with something like
   std::vector<int> v;

    auto t2 = r | transformed( [](int) {return 0;} );
    auto p2 = boost::range::partition(t2, [](int) {return true;} ); , but that didn't work. On Stackoverflow, it was explained that this doesn't work because partition needs to modify the range, and a transformed range is not modifiable. So far so good, I can follow this and see why and modify the program to use transform on the vector directly.

What bothers me is that I was not able to figure that out from the documentation, and that the error message was not very intuitive to say the least. According to the documentation, the requirements on the range for partition are that it has to be a model of ForwardRange, which means that the iterators have to be forward traversable iterators. I think the important fact, namely that it has to be writeable iterator, is missing from the documentation completely. As far as I can see, readable/writable categories are not used in the range documentation at all.

Best wishes,
  Jens

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