26 Numerics library [numerics]

26.7 Numeric arrays [numarray]

26.7.9 Class template indirect_­array [template.indirect.array]

26.7.9.1 Overview [template.indirect.array.overview]

namespace std {
  template<class T> class indirect_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;

    indirect_array(const indirect_array&);
    ~indirect_array();
    const indirect_array& operator=(const indirect_array&) const;
    void operator=(const T&) const;

    indirect_array() = delete;  // as implied by declaring copy constructor above
  };
}
1
#
This template is a helper template used by the indirect subscript operator
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indirect_array<T> valarray<T>::operator[](const valarray<size_t>&).
2
#
It has reference semantics to a subset of an array specified by an indirect_­array.
Thus, the expression a[​indirect] = b; has the effect of assigning the elements of b to the elements in a whose indices appear in indirect.

26.7.9.2 Assignment [indirect.array.assign]

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void operator=(const valarray<T>&) const; const indirect_array& operator=(const indirect_array&) const;
1
#
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.
2
#
If the indirect_­array specifies an element in the valarray<T> object to which it refers more than once, the behavior is undefined.
3
#
[Example
: 
int addr[] = {2, 3, 1, 4, 4};
valarray<size_t> indirect(addr, 5);
valarray<double> a(0., 10), b(1., 5);
a[indirect] = b;
results in undefined behavior since element 4 is specified twice in the indirection.
— end example
]

26.7.9.3 Compound assignment [indirect.array.comp.assign]

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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;
1
#
These compound assignments have reference semantics, applying the indicated operation to the elements of the argument array and selected elements of the valarray<T> object to which the indirect_­array object refers.
2
#
If the indirect_­array specifies an element in the valarray<T> object to which it refers more than once, the behavior is undefined.

26.7.9.4 Fill function [indirect.array.fill]

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void operator=(const T&) const;
1
#
This function has reference semantics, assigning the value of its argument to the elements of the valarray<T> object to which the indirect_­array object refers.