C++

Reference

<valarray>

class template
<valarray>

std::indirect_array

template <class T> indirect_array;
Valarray indirect selection
This class is used as an intermediate type returned by valarray's subscript operator (operator[]) when used with a valarray of indices.

It references the elements from the valarray whose index is included in the object passed to the subscript operator.

The type is convertible to a valarray (see valarray constructor), producing a new object with copies of the referred elements.

Objects of this type are obtained as the return value of a call to valarray::operator[]. They cannot be directly constructed nor copied. It is declared as:

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template <class T> class indirect_array {
public:
  typedef T value_type;
  void operator=   (const valarray<T>&) const;
  void operator*=  (const valarray<T>&) const;
  void operator/=  (const valarray<T>&) const;
  void operator%=  (const valarray<T>&) const;
  void operator+=  (const valarray<T>&) const;
  void operator-=  (const valarray<T>&) const;
  void operator^=  (const valarray<T>&) const;
  void operator&=  (const valarray<T>&) const;
  void operator|=  (const valarray<T>&) const;
  void operator<<= (const valarray<T>&) const;
  void operator>>= (const valarray<T>&) const;
  void operator=(const T&);
  ~indirect_array();
private:
  indirect_array();
  indirect_array(const indirect_array&);
  indirect_array& operator= (const indirect_array&);
};
Objects of this type are obtained as the return value of a call to valarray::operator[]. They cannot be default-constructed, but can be copied. It is declared as:

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template <class T> class indirect_array {
public:
  typedef T value_type;
  void operator=   (const valarray<T>&) const;
  void operator*=  (const valarray<T>&) const;
  void operator/=  (const valarray<T>&) const;
  void operator%=  (const valarray<T>&) const;
  void operator+=  (const valarray<T>&) const;
  void operator-=  (const valarray<T>&) const;
  void operator^=  (const valarray<T>&) const;
  void operator&=  (const valarray<T>&) const;
  void operator|=  (const valarray<T>&) const;
  void operator<<= (const valarray<T>&) const;
  void operator>>= (const valarray<T>&) const;
  void operator=(const T&);

  indirect_array() = delete;
  indirect_array(const gslice_array&);
  const indirect_array& operator= (const indirect_array&) const;
  ~indirect_array();
};

Example

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// indirect_array example
#include <iostream>     // std::cout
#include <cstddef>      // std::size_t
#include <valarray>     // std::valarray

int main ()
{
  std::valarray<int> foo (8);
  for (int i=0; i<8; ++i) foo[i]=i;             //  0  1  2  3  4  5  6  7

  std::size_t sel[] = {3,5,6};
  std::valarray<std::size_t> selection (sel,3); //           *     *  *

  foo[selection] *= std::valarray<int>(10,3);   //  0  1  2 30  4 50 60 7
  foo[selection] = 0;                           //  0  1  2  0  4  0  0 7

  std::cout << "foo:";
  for (std::size_t i=0; i<foo.size(); ++i)
    std::cout << ' ' << foo[i];
  std::cout << '\n';

  return 0;
}

Output:

foo: 0 1 2 0 4 0 0 7


See also

slice_array
Valarray slice selection (class template)
gslice_array
Valarray gslice selection (class template)
mask_array
Valarray mask selection (class template)