lar::CollectionView< Range > Class Template Reference

Provides features of a collections, from begin and end iterators. More...

#include "CollectionView.h"

Inheritance diagram for lar::CollectionView< Range >:

Public Types
using	collection_type = range_t
	Type of collection being wrapped. More...
using	value_type = typename iter_traits_t::value_type
using	const_reference = typename iter_traits_t::reference
using	const_pointer = typename iter_traits_t::pointer
using	const_iterator = begin_iter_t
using	const_reverse_iterator = std::reverse_iterator< const_iterator >
using	difference_type = typename iter_traits_t::difference_type
using	size_type = std::size_t

Public Member Functions
Forward access.
bool	empty () const noexcept
	Returns whether the collection is empty. More...
size_type	size () const noexcept
	Returns the size of the collection. More...
const_iterator	cbegin () const noexcept
	Returns an iterator to the begin of the collection. More...
end_iter_t	cend () const noexcept
	Returns an iterator past the end of the collection. More...
const_iterator	begin () const noexcept
	Returns an iterator to the begin of the collection. More...
end_iter_t	end () const noexcept
	Returns an iterator past the end of the collection. More...
auto	front () const -> decltype(auto)
	Returns the first element in the collection. More...
Backward access.
const_reverse_iterator	rbegin () const noexcept
	Returns a reverse iterator to the begin of the collection. More...
const_reverse_iterator	rend () const noexcept
	Returns a reverse iterator past the end of the collection. More...
const_reverse_iterator	crbegin () const noexcept
	Returns a reverse iterator to the begin of the collection. More...
const_reverse_iterator	crend () const noexcept
	Returns a reverse iterator past the end of the collection. More...
auto	back () const -> decltype(auto)
	Returns the last element in the collection. More...
Random access.
auto	operator[] (size_type i) const -> decltype(auto)
	Returns the content of the i-th element. More...
auto	at (size_type i) const -> decltype(auto)
	Returns the content of the i-th element. More...
Contiguous access.
const_pointer	data () const

Protected Member Functions
	CollectionView (range_t &&range)
	Constructor: steals the data from the specified range. More...

Private Types
using	this_t = CollectionView< Range >
	This type. More...
using	range_t = Range
	Type of the range being wrapped. More...
using	traits_t = details::RangeTraits< range_t >
	Range traits. More...
using	begin_iter_t = typename traits_t::begin_iterator_t
	Type of the begin iterator. More...
using	end_iter_t = typename traits_t::end_iterator_t
	Type of the end iterator. More...
using	iter_traits_t = std::iterator_traits< begin_iter_t >
	Type of traits of iterator. More...

Private Member Functions
range_t const &	asRange () const
	Returns this very object, cast back to range_t. More...

Friends
this_t	details::makeCollectionView (range_t &&)

Detailed Description

template<typename Range>
class lar::CollectionView< Range >

Provides features of a collections, from begin and end iterators.

Template Parameters

Range

the type of collection to be wrapped

A collection view is a class that offers a collection-like interface, mostly like the C+ standard library containers, based on two iterators.

The base, wrapped collection is required to respond to begin() and a end() global functions. If the desired view is not described by such an object, a temporary one must be created (see makeCollectionView()).

There are two ways to use this class:

1. to wrap an existing Range-like container
2. to turn two iterators into a container

The two use cases are both addressed by this class, but helper functions are provided to make it easier to create them as needed.

Note

While the object is currently copiable and moveable, this is not guaranteed for the future.

Wrap an existing Range-like container

Here we assume there is somewhere an instance of the object range which fulfills the requirement of the Range type above, that is it responds to the requests of a begin() and a end() iterator.

To create a collection view of range, the easiest way is to use wrapCollectionIntoView(). In the following example the range object is a STL vector (which does not really need any added interface...):

std::vector<int> range(5);
std::iota(range.begin(), range.end(), 1); // { 1, 2, 3, 4, 5 }

for (int d: lar::wrapCollectionIntoView(range)) {
  std::cout << d << " ";
}
std::cout << std::endl;

which will print "1 2 3 4 5 ". Here the wrapped collection object, returned by wrapCollectionIntoView(), is insubstantial. It can be saved with

decltype(auto) view = lar::wrapCollectionIntoView(range);

or even:

auto const& view = lar::wrapCollectionIntoView(range);

but it will be just a (constant) reference to something else.

Turn two iterators into a container

In this approach, we have two iterators to an existing collection, and we want to use them as extremes of a "virtual" collection. Again we use a STL vector as a base container for the example. Here we want to see a subrange of it as a new collection. We use makeCollectionView().

std::vector<int> v(10);
std::iota(v.begin(), v.end(), 0); // { 0, 1, ..., 9 }

for (int d: lar::makeCollectionView(v.begin() + 4, v.begin() + 7)) {
  std::cout << d << " ";
}
std::cout << std::endl;

will print "0 1 2 3 4 5 6 7 8 9 ".

Declaring a wrapper class

The function lar::makeCollectionView() creates a view owning the information the view requires. Similarly, a new class can be defined which does the same, by simply deriving it from lar::CollectionView:

class IntVector {
   using vector_t = std::vector<int>;

   vector_t data;

     public:
   IntVector(vector_t&& data): data(std::move(data)) {}

   auto begin() const -> decltype(auto) { return data.cbegin(); }
   auto end() const -> decltype(auto) { return data.cend(); }

}; // struct IntVector

using IntViewBase_t = lar::CollectionView<IntVector>;

struct MyCollection: public IntViewBase_t {
  MyCollection(std::vector<int>&& data) : IntViewBase_t(std::move(data)) {}
}; // class MyCollection

aftter which MyCollection interface can be enriched as needed. The IntViewBase_t alias is a way to overcome the fact that the name IntVector can't be used inside MyCollection because it's actually a private base class (the base class, even if not direct, will hide IntVector, even if, being private, it can't even be used). Another way is to fully qualify its name (e.g. ::IntVector).

Note that to avoid accidental copies, lar::CollectionView objects can't be directly instantiated: using directly IntViewBase_t will not be allowed.

Definition at line 98 of file CollectionView.h.

Member Typedef Documentation

template<typename Range>

using lar::CollectionView< Range >::begin_iter_t = typename traits_t::begin_iterator_t

private

Type of the begin iterator.

Definition at line 292 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::collection_type = range_t

Type of collection being wrapped.

Definition at line 300 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::const_iterator = begin_iter_t

Definition at line 308 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::const_pointer = typename iter_traits_t::pointer

Definition at line 306 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::const_reference = typename iter_traits_t::reference

Definition at line 304 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::const_reverse_iterator = std::reverse_iterator<const_iterator>

Definition at line 310 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::difference_type = typename iter_traits_t::difference_type

Definition at line 311 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::end_iter_t = typename traits_t::end_iterator_t

private

Type of the end iterator.

Definition at line 294 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::iter_traits_t = std::iterator_traits<begin_iter_t>

private

Type of traits of iterator.

Definition at line 297 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::range_t = Range

private

Type of the range being wrapped.

Definition at line 288 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::size_type = std::size_t

Definition at line 312 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::this_t = CollectionView<Range>

private

This type.

Definition at line 287 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::traits_t = details::RangeTraits<range_t>

private

Range traits.

Definition at line 289 of file CollectionView.h.

template<typename Range>

using lar::CollectionView< Range >::value_type = typename iter_traits_t::value_type

Definition at line 302 of file CollectionView.h.

Constructor & Destructor Documentation

template<typename Range>

lar::CollectionView< Range >::CollectionView ( range_t &&  range )

inlineexplicitprotected

Constructor: steals the data from the specified range.

Definition at line 408 of file CollectionView.h.

: range_t(std::move(range)) {}

Member Function Documentation

template<typename Range>

range_t const& lar::CollectionView< Range >::asRange ( ) const

inlineprivate

Returns this very object, cast back to range_t.

Definition at line 416 of file CollectionView.h.

      { return static_cast<range_t const&>(*this); }

template<typename Range>

auto lar::CollectionView< Range >::at ( size_type  i ) const -> decltype(auto)

inline

Returns the content of the i-th element.

Definition at line 372 of file CollectionView.h.

      {
        if (i >= size()) {
          throw std::out_of_range(
            "CollectionView index out of range: "
            + std::to_string(i) + " >= " + std::to_string(size())
            );
        }
        return operator[](i);
      }

template<typename Range>

auto lar::CollectionView< Range >::back ( ) const -> decltype(auto)

inline

Returns the last element in the collection.

Definition at line 360 of file CollectionView.h.

{ return *crbegin(); }

template<typename Range>

const_iterator lar::CollectionView< Range >::begin ( ) const

inlinenoexcept

Returns an iterator to the begin of the collection.

Definition at line 332 of file CollectionView.h.

{ return cbegin(); }

template<typename Range>

const_iterator lar::CollectionView< Range >::cbegin ( ) const

inlinenoexcept

Returns an iterator to the begin of the collection.

Definition at line 324 of file CollectionView.h.

      { using std::cbegin; return cbegin(asRange()); }

template<typename Range>

end_iter_t lar::CollectionView< Range >::cend ( ) const

inlinenoexcept

Returns an iterator past the end of the collection.

Definition at line 328 of file CollectionView.h.

      { using std::cend; return cend(asRange()); }

template<typename Range>

const_reverse_iterator lar::CollectionView< Range >::crbegin ( ) const

inlinenoexcept

Returns a reverse iterator to the begin of the collection.

Definition at line 352 of file CollectionView.h.

      { return const_reverse_iterator(cend()); }

template<typename Range>

const_reverse_iterator lar::CollectionView< Range >::crend ( ) const

inlinenoexcept

Returns a reverse iterator past the end of the collection.

Definition at line 356 of file CollectionView.h.

      { return const_reverse_iterator(cbegin()); }

template<typename Range>

const_pointer lar::CollectionView< Range >::data ( ) const

inline

Definition at line 388 of file CollectionView.h.

{ return &front(); }

template<typename Range>

bool lar::CollectionView< Range >::empty ( ) const

inlinenoexcept

Returns whether the collection is empty.

Definition at line 318 of file CollectionView.h.

{ return cbegin() == cend(); }

template<typename Range>

end_iter_t lar::CollectionView< Range >::end ( ) const

inlinenoexcept

Returns an iterator past the end of the collection.

Definition at line 335 of file CollectionView.h.

{ return cend(); }

template<typename Range>

auto lar::CollectionView< Range >::front ( ) const -> decltype(auto)

inline

Returns the first element in the collection.

Definition at line 338 of file CollectionView.h.

{ return *cbegin(); }

template<typename Range>

auto lar::CollectionView< Range >::operator[] ( size_type  i ) const -> decltype(auto)

inline

Returns the content of the i-th element.

Definition at line 368 of file CollectionView.h.

      { return cbegin()[i]; }

template<typename Range>

const_reverse_iterator lar::CollectionView< Range >::rbegin ( ) const

inlinenoexcept

Returns a reverse iterator to the begin of the collection.

Definition at line 346 of file CollectionView.h.

{ return crbegin(); }

template<typename Range>

const_reverse_iterator lar::CollectionView< Range >::rend ( ) const

inlinenoexcept

Returns a reverse iterator past the end of the collection.

Definition at line 349 of file CollectionView.h.

{ return crend(); }

template<typename Range>

size_type lar::CollectionView< Range >::size ( ) const

inlinenoexcept

Returns the size of the collection.

Definition at line 321 of file CollectionView.h.

{ return std::distance(cbegin(), cend()); }

Friends And Related Function Documentation

template<typename Range>

this_t details::makeCollectionView ( range_t &&  )

friend

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The documentation for this class was generated from the following file:

• /cvmfs/larsoft.opensciencegrid.org/products/lardata/v07_01_01/source/lardata/Utilities/CollectionView.h