What is a range

A range is anything that can be iterate. Typically in C++ something is a range if we can call begin(range) and end(range) on it.

How to create a range

In rah this is done by rah::iterator_range. Two way to create an iterator_range:

rah::iterator_range<iterator_type>(begin_iter, end_iter);
rah::make_iterator_range (begin_iter, end_iter);

What is a view

A view is a range returned by a function an which doesn't modify it's input range.
The computing is often done in a "lazy" way, that is to say at the moment of iteration.
There is two kind of view:

Views which take a range and give a modified view on it:
- Example: rah::view::filter, rah::view::transform
Generators
- Example: rah::view::iota, rah::view::generate

How to make a view

To make a view you have to create an iterator.
- For example the rah::view::filter view is an rah::iterator_range of rah::view::filter_iterator.
Then you have to create a function taking a range and parameters (or no range for generator)

template<typename R> auto retro(R&& range)
{
    return make_iterator_range(
        std::make_reverse_iterator(end(range)), std::make_reverse_iterator(begin(range)));
}

Then you can add a pipeable version of the function

auto retro()
{
    return make_pipeable([=](auto&& range) {return retro(range); });
}

How to make an iterator

There is in rah an helper to create iterators: rah::iterator_facade There are three kind of rah::iterator_facade:

rah::iterator_facade<I, R, std::forward_iterator_tag>
- For an example : rah::view::generate_iterator
rah::iterator_facade<I, R, std::bidirectional_iterator_tag >
- For an example : rah::view::zip_iterator
rah::iterator_facade<I, R, std::random_access_iterator_tag>
- For an example : rah::view::iota_iterator

How to make a pipeable view or algorithm

Use the rah::make_pipeable function.

How to create a pipeable :

auto test_count(int i)
{
    return rah::make_pipeable([=](auto&& range) { return std::count(begin(range), end(range), i); });
}

How to use a pipeable :

std::vector<int> vec{ 0, 1, 2, 2, 3 };

assert((vec | test_count(2)) == 2);