https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109400
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
For ranges::advance we could do something like this, but it feels like there
should be a better way to customize ranges::advance for your own iterators:
--- a/libstdc++-v3/include/bits/ranges_base.h
+++ b/libstdc++-v3/include/bits/ranges_base.h
@@ -712,6 +712,12 @@ namespace ranges
struct __advance_fn final
{
+ template<typename _Tp>
+ constexpr bool __is_istreambuf_iter = false;
+ template<typename _CharT>
+ constexpr bool __is_istreambuf_iter<std::istreambuf_iterator<_CharT>>
+ = __gnu_cxx::__is_char<_CharT>::__value;
+
template<input_or_output_iterator _It>
constexpr void
operator()(_It& __it, iter_difference_t<_It> __n) const
@@ -737,6 +743,8 @@ namespace ranges
while (++__n);
}
}
+ else if constexpr (__is_istreambuf_iter<_It>)
+ std::advance(__it, __n);
else
{
// cannot decrement a non-bidirectional iterator
@@ -754,6 +762,9 @@ namespace ranges
__it = std::move(__bound);
else if constexpr (sized_sentinel_for<_Sent, _It>)
(*this)(__it, __bound - __it);
+ else if constexpr (__is_istreambuf_iter<_It>
+ && is_same_v<_Sent, default_sentinel_t>)
+ __it = _It();
else
{
while (__it != __bound)
@@ -791,6 +802,11 @@ namespace ranges
return __n;
else if (__n > 0)
{
+ if constexpr (__is_istreambuf_iter<_It>)
+ {
+ // TODO need access to __it._M_sbuf
+ }
+
iter_difference_t<_It> __m = 0;
do
{
