range-v3

I want to use an existing view for concatenation. In code: auto rng = view::empty<vector<int>>(); for(int i{0}; i < 5; ++i) { vector<int> const & v{foo()}; // returns a reference rng |= view::concat(v); // doesn't compile - error: no viable overloaded '|=' }; In other words - how can I create a view to multiple vectors whose number is not known until runtime? You can't compose views this way. Concatenating a view yields an object with a different type. You can't assign it back to the original view because its type is different. You can get the effect you're after with a combination of view:

This question follows a discussion in the comments here . In Eric Niebler's ranges-v3 library (which is sort-of becoming part of the standard for C++20), ranges::ostream_iterator is default-constructible - without an ostream. How come? I thought that "dummy" construction with effective construction later is an anti-pattern in C++, a wart we are gradually getting rid of. std::ostream iterator can only be constructed with a stream (for now - before C++20). And it's not as though we can do anything with the default-constructed range::ostream_iterator ... So, what's the deal? This follows the

I have a third-party function with this signature: std::vector<T> f(T t); I also have an existing potentially infinite range ( of the range-v3 sort ) of T named src . I want to create a pipeline that maps f to all elements of that range and flattens all the vectors into a single range with all their elements. Instinctively, I would write the following. auto rng = src | view::transform(f) | view::join; However, this won't work, because we cannot create views of temporary containers. How does range-v3 support such a range pipeline? I suspect it just can't. None of the view s have any machinery