26 Numerics library [numerics]

26.6 Numeric arrays [numarray]

26.6.9 Class template indirect_array [template.indirect.array]

26.6.9.2 indirect_array assignment [indirect.array.assign]

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 ]