Given a type
T and a subexpression
E of type
U,
if
U models
derived_from<basic_istream<typename U::char_type,
typename U::traits_type>>,
then the expression
views::istream<T>(E) is expression-equivalent to
basic_istream_view<T, typename U::char_type,
typename U::traits_type>(E);
otherwise,
views::istream<T>(E) is ill-formed
.