https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116399
--- Comment #19 from Jonathan Wakely <redi at gcc dot gnu.org> ---
We could do this, and rely on the fact that the number of aliases is always
small so that we can claim it's O(1):
--- a/libstdc++-v3/include/std/text_encoding
+++ b/libstdc++-v3/include/std/text_encoding
@@ -644,6 +644,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return __i;
}
+ friend constexpr difference_type
+ operator-(_Sentinel __s, _Iterator __i)
+ {
+ __glibcxx_assert(__i._M_rep != nullptr);
+ difference_type __n = 0;
+ if (const _Rep* __rep = __i._M_rep)
+ while (__rep[__n]._M_id == __i._M_id)
+ ++__n;
+ return __n;
+ }
+
+ friend constexpr difference_type
+ operator-(_Iterator __i, _Sentinel __s)
+ { return -(__s - __i); }
+
private:
friend struct text_encoding;
