Make images & views model Collection concept.

[john.femiani@…]

It would be convenient if GIL views modeled ReversibleCollection concept. In fact they almost do already.

Without modeling this concept, it is hard to use an image view with boost::range algorithms.

Suggested patch:

image_view.hpp

@@ -82 +82 @@
         typedef typename Loc::template axis<D>::iterator iterator;       // 1D iterator type along each dimension
     };
     typedef iterator_from_2d<Loc>                    iterator;       // 1D iterator type for each pixel left-to-right inside top-to-bottom
+    typedef typename const_t::iterator               const_iterator;
+    typedef typename const_t::reference              const_reference;
+    typedef typename std::iterator_traits<iterator>::pointer pointer;
     typedef std::reverse_iterator<iterator>          reverse_iterator;
     typedef std::size_t                              size_type;
 
@@ -111 +114 @@
 
     template <typename L2> friend void swap(image_view<L2>& x, image_view<L2>& y);
 
+    ///\brief Exchanges the elements of the current view with those of \a other
+    ///       in constant time.
+    ///
+    ///\note Required by concept
+    ///      http://www.boost.org/doc/libs/1_35_0/libs/utility/Collection.html
+    void swap(image_view<Loc>& other)
+    {
+        swap(*this, other);
+    }
+
+
+
+    ///\brief Returns true if the view has no elements, false otherwise.
+    ///
+    ///\note Required by concept
+    ///      http://www.boost.org/doc/libs/1_35_0/libs/utility/Collection.html
+    bool empty() const
+    {
+        return width() > 0 && height() > 0;
+    }
+
+    ///\brief Returns a reference to the first element in raster order.
+    ///
+    ///\note Required by concept
+    ///      http://www.boost.org/doc/libs/1_35_0/libs/utility/Collection.html
+    ///      since views model ForwardCollection
+    reference front() const
+    {
+        return *begin();
+    }
+
+    ///\brief Returns a reference to the last element in raster order.
+    ///
+    ///\note Required by concept
+    ///      http://www.boost.org/doc/libs/1_35_0/libs/utility/Collection.html
+    ///      since views model ReversibleCollection
+    reference back() const
+    {
+        return *rbegin();
+    }
+
     const point_t&   dimensions()            const { return _dimensions; }
     const locator&   pixels()                const { return _pixels; }
     x_coord_t        width()                 const { return dimensions().x; }

[Mateusz Loskot]

I believe, this condition

129	    ///\brief Returns true if the view has no elements, false otherwise.
130	    ///
131	    ///\note Required by concept
132	    ///      http://www.boost.org/doc/libs/1_35_0/libs/utility/Collection.html
133	    bool empty() const
134	    {
135	        return width() > 0 && height() > 0;
136	    }

should read

return !(width() > 0 && height() > 0);

[Mateusz Loskot]

Moved to ​https://github.com/boostorg/gil/pull/133

Submited as PR against the current develop branch, with additions.

Thanks for the suggestion and patch!

[Mateusz Loskot]

The suggestion has been merged via ​​https://github.com/boostorg/gil/pull/133 and should be released with Boost 1.69