[template.mask.array.overview] (original) (raw)

29 Numerics library [numerics]

29.6 Numeric arrays [numarray]

29.6.8 Class template mask_array [template.mask.array]

29.6.8.1 Overview [template.mask.array.overview]

namespace std { template<class T> class mask_array { public: using value_type = T;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; mask_array(const mask_array&);~mask_array();const mask_array& operator=(const mask_array&) const;void operator=(const T&) const; mask_array() = delete; };}

This template is a helper template used by the mask subscript operator:

mask_array<T> valarray<T>::operator[](const valarray<bool>&);

It has reference semantics to a subset of an array specified by a boolean mask.

Thus, the expression a[mask] = b;has the effect of assigning the elements ofb to the masked elements in a(those for which the corresponding element inmask is true).