std::indirect_array(3)

NAME
std::indirect_array - std::indirect_array

Synopsis
   Defined in header <valarray>
   template< class T > class indirect_array;
   std::indirect_array is a helper template used by the valarray subscript operator
   with std::valarray<std::size_t> argument. It has reference semantics to a subset of
   the array whose indices specified by the std::valarray<std::size_t> object.

Member types
   Type Definition
   value_type T

Member functions
   constructor constructs a indirect_array
                 (public member function)
   destructor destroys a indirect_array
                 (public member function)
   operator= assigns contents
                 (public member function)
   operator+=
   operator-=
   operator*=
   operator/=
   operator%= performs arithmetic operation on the array referred by indirect array.
   operator&= (public member function)
   operator|=
   operator^=
   operator<<=
   operator>>=

Example
// Run this code
 #include <iostream>
 #include <valarray>
 int main()
 {
     std::valarray<int> data{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
     std::valarray<std::size_t> idx{0, 2, 4, 6, 8};
     std::cout << "Original valarray: ";
     for (int n : data)
         std::cout << n << ' ';
     std::cout << '\n';
     data[idx] += data[idx]; // double the values at indices 'idx'
     // the type of data[idx] is std::indirect_array<int>
     std::cout << "After indirect modification: ";
     for (int n : data)
         std::cout << n << ' ';
     std::cout << '\n';
 }

Output:
 Original valarray: 0 1 2 3 4 5 6 7 8 9
 After indirect modification: 0 1 4 3 8 5 12 7 16 9