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copied!<p>From the table of <a href="http://www.boost.org/doc/libs/1_45_0/libs/multi_array/doc/reference.html#id835500" rel="noreferrer">MultiView associated types</a>:</p> <blockquote> <p>reference This is the reference type of the contained value. If NumDims == 1, then this is element&. Otherwise, this is the same type as template subarray::type.</p> <p>template array_view::type This is the view type with Dims dimensions. It is returned by calling operator. It models MultiArray.</p> </blockquote> <p>so they're different types, to start with. In this context, views represent a sort of subcollection of a MultiArray. They implement the MultiArray concept, but the elements they contain are actually elements of some other MultiArray. Views allow you to define a new <a href="http://live.boost.org/doc/libs/1_34_0/libs/multi_index/doc/reference/indices.html" rel="noreferrer">index</a> into the elements of a MultiArray. For example, you could define a view that reverses the index, so that the first element of the view is the last element of the MultiArray. From the <a href="http://www.boost.org/doc/libs/1_45_0/libs/multi_array/doc/reference.html#MultiArray" rel="noreferrer">documentation</a>:</p> <blockquote> <p>A view lets you treat a subset of the underlying elements in a MultiArray as though it were a separate MultiArray. Since a view refers to the same underlying elements, changes made to a view's elements will be reflected in the original MultiArray.</p> </blockquote> <p>MultiArrays are defined recursively; a MultiArray of dimension <em>n</em> > 1 can be thought of as array of MultiArrays of dimension <em>n</em>-1, which are subarrays. The key difference between a subarray and a view is that you can slice a MultiArray into views of lower dimensions along any axis, including the major axis, but subarrays cannot be sliced along the major axis.</p> <pre><code>data_t d3(boost::extents[4][5][6]); data_2d_view_t d2_view = d3[boost::indices[range(0,4,2)][1][range(0,6,3)]]; data_2d_subarray_t d2_sub = d3[1]; // the following, and anything like it, won't work data_2d_subarray_t d2_sub_b = d3[range(0,4,2)][0]; </code></pre> <p>I don't believe there's any major performance difference, though this depends on what type of index you use when creating a view. Views might be slightly less performant, but not in a big-O sense.</p>

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