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std::mask_array(3)	       C++ Standard Libary	      std::mask_array(3)

NAME
     std::mask_array - std::mask_array

Synopsis
	Defined in header <valarray>
	template< class T > class mask_array;

	std::mask_array  is a helper template used by the valarray subscript op-
     erator with
	std::valarray<bool> argument. It has reference	semantics  and	provides
     access to the
	subset	of  the valarray consisting of the elements whose indices corre-
     spond to true
	values in the std::valarray<bool> mask.

Member types
	Type	   Definition
	value_type T

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

Example
     // Run this code

      #include <iostream>
      #include <valarray>

      void println(auto rem, const auto& data)
      {
	  for (std::cout << rem; int n : data)
	      std::cout << n << ' ';
	  std::cout << '\n';
      }

      int main()
      {
	  std::valarray<int> data{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};

	  println("Initial valarray: ", data);

	  data[data > 5] = -1;
	  // the type of data>5 is std::valarray<bool>
	  // the type of data[data>5] is std::mask_array<int>

	  println("After v[v>5]=-1:  ", data);
      }

Output:
      Initial valarray: 0 1 2 3 4 5 6 7 8 9
      After v[v>5]=-1:	0 1 2 3 4 5 -1 -1 -1 -1

See also
	simd_mask	    data-parallel type with the element type bool
	(parallelism TS v2) (class template)

http://cppreference.com 	   2024.06.10		      std::mask_array(3)
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