24 Numerics library [numerics]

24.8 Numeric arrays [numarray]

24.8.8 Class template mask_­array [template.mask.array]

24.8.8.2 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.