Sorter traits

#include <cpp-sort/sorter_traits.h>

is_sorter and friends

These variable templates is_sorter<typename Sorter, typename Iterable> and is_comparison_sorter<typename Sorter, typename Iterable, typename Compare> respectively equal true if the type Sorter satisfies the sorter concept or the ComparisonSorter concept and equals false otherwise.

In our case, a Sorter is a type that can be called with an Iterable& while a ComparisonSorter is a that can be called with an Iterable& and a Compare. These traits mainly exist for SFINAE purpose and concept checking.

template<typename Sorter, typename Iterable>
constexpr bool is_sorter = /* implementation-defined */;

template<typename Sorter, typename Iterable, typename Compare>
constexpr bool is_comparison_sorter = /* implementation-defined */;

There are also variants of these variable templates which take a potential sorter type and an iterator type. These exist to check whether the sorter can be called with a pair of iterators.

template<typename Sorter, typename Iterator>
constexpr bool is_sorter_iterator = /* implementation-defined */;

template<typename Sorter, typename Iterator, typename Compare>
constexpr bool is_comparison_sorter_iterator = /* implementation-defined */;

sorter_traits

The class template sorter_traits<Sorter> contains information about sorters and sorter adapters such as the kind of iterators accepted by a sorter and whether it implements or not a stable sorting algorithm.

template<typename Sorter>
struct sorter_traits {};

This class can be specialized for every sorter object and contains the following fields:

• using iterator_category = /* depends on the sorter */;
• static constexpr bool is_stable = /* depends on the context */;

The non-specialized version of sorter_traits is defined but empty for SFINAE friendliness.

iterator_category

template<typename Sorter>
using iterator_category = typename sorter_traits<Sorter>::iterator_category;

Some tools need to know which category of iterators a sorting algorithm can work with. Therefore, a well-defined sorter provides one of the standard library iterator tags in order to document that.

When a sorter is adapted so that it may be used with several categories of iterators, the resulting sorter's iterator category will correspond to the most permissive. For example, if an hybrid_sorter merges sorting algorithms with std::forward_iterator_tag and std::random_access_iterator_tag, then the resulting sorter's category will be std::forward_iterator_tag since it is guaranteed to work with any iterable type which has at least forward iterators.

is_stable

template<typename Sorter>
constexpr bool is_stable = sorter_traits<Sorter>::is_stable;

This variable template contains a boolean value which tells whether a sorting algorithm is stable or not. This information may be useful in some contexts.

When a sorter adapter is used, the stability of the resulting sorter is true if and only if its stability can be guaranteed and false otherwise, even when the adapted sorter may be stable (for example, self_sorter is always false since you can't guarantee its stability).

rebind_iterator_category

template<typename Sorter, typename Category>
struct rebind_iterator_category;

This class allows to get a sorter similar to the one passed but with a stricter iterator category. For example, it can generate a sorter whose iterator category is std::bidirectional_iterator_tag from another sorter whose iterator category is std::forward_iterator_tag. It is mostly ueful to make several sorters with the same iterator category work work for different iterator categories in an hybrid_adapter. Let's say we have two sorters, foo_sorter and bar_sorter; both have the iterator category std::forward_iterator_tag, but foo_sorter is the best to sort forward iterators while bar_sorter is benefits from some optimizations for bidirectional and random-access iterators. It is possible to use the best of both with the following sorter:

using sorter = cppsort::hybrid_adapter<
    foo_sorter,
    cppsort::rebind_iterator_category<
        bar_sorter,
        std::bidirectional_iterator_tag
    >
>;

The sorter above will pick foo_sorter for forward iterators, but it will pick bar_sorter for bidirectional and random-access iterators. A compile-time error will occur if one tries to rebind to an iterator category that is not derived from the sorter's original iterator category.