In the begin and end function templates that follow, unspecified1 is a type that meets the requirements of a mutable random access iterator ([random.access.iterators]) and of a contiguous iterator ([iterator.requirements.general]) whose value_type is the template parameter T and whose reference type is T&. unspecified2 is a type that meets the requirements of a constant random access iterator ([random.access.iterators]) and of a contiguous iterator ([iterator.requirements.general]) whose value_type is the template parameter T and whose reference type is const T&.
The iterators returned by begin and end for an array are guaranteed to be valid until the member function resize(size_t, T) ([valarray.members]) is called for that array or until the lifetime of that array ends, whichever happens first.
template <class T> unspecified1 begin(valarray<T>& v);
template <class T> unspecified2 begin(const valarray<T>& v);
Returns: An iterator referencing the first value in the numeric array.
template <class T> unspecified1 end(valarray<T>& v);
template <class T> unspecified2 end(const valarray<T>& v);
Returns: An iterator referencing one past the last value in the numeric array.