26 Numerics library [numerics]

26.6 Numeric arrays [numarray]

26.6.8 Class template mask_array [template.mask.array]

26.6.8.2 mask_array assignment [mask.array.assign]

void operator=(const valarray<T>&) const; const mask_array& operator=(const mask_array&) const;

These assignment operators have reference semantics, assigning the values of the argument array elements to selected elements of the valarray<T> object to which it refers.