nview

Description

nview presents a view which iterates over a given Sequence in a specified order. An nview is constructed from an arbitrary Sequence and a list of indices specifying the elements to iterate over.

Header

#include <boost/fusion/view/nview.hpp>
#include <boost/fusion/include/nview.hpp>

Synopsis

template <typename Sequence, typename Indices>
struct nview;

template <typename Sequence, int I1, int I2 = -1, ...>
typename result_of::nview<Sequence, I1, I2, ...>::type
as_nview(Sequence& s);

Template parameters

Parameter	Description	Default
`Sequence`	An arbitrary Fusion Forward Sequence
`Indices`	A `mpl::vector_c<int, ...>` holding the indices defining the required iteration order.
`I1`, `I2`, `I3`...	A list of integers specifying the required iteration order.	`INT_MAX` for `I2`, `I3`...

Model of

Random Access Sequence (see Sequence Traversal Concept)

Notation

NV: A nview type
s: An instance of Sequences
nv1, nv2: Instances of NV

Expression Semantics

Semantics of an expression is defined only where it differs from, or is not defined in Random Access Sequence.

Expression	Semantics
`NV(s)`	Creates an `nview` given a sequence and a list of indices.
`NV(nv1)`	Copy constructs an `nview` from another `nview`, `nv1`.
`nv1 = nv2`	Assigns to an `nview`, `nv1`, from another `nview`, `nv2`.

The nview internally stores a Fusion vector of references to the elements of the original Fusion Sequence

Example

typedef vector<int, char, double> vec;
typedef mpl::vector_c<int, 2, 1, 0, 2, 0> indices;

vec v1(1, 'c', 2.0);

std::cout << nview<vec, indices>(v1) << std::endl; // (2.0 c 1 2.0 1)
std::cout << as_nview<2, 1, 1, 0>(v1) << std::endl; // (2.0 c c 1)