https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105841
Jason Merrill <jason at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |NEW
CC| |mike at spertus dot com
Assignee|jason at gcc dot gnu.org |unassigned at gcc dot
gnu.org
--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
In alias_ctad_tweaks, I wrote:
/* This implementation differs from the [standard] in two significant ways:
1) We include all template parameters of A, not just some.
2) The added constraint is same_type instead of deducible.
I believe that while it's probably possible to construct a testcase that
behaves differently with this simplification, it should have the same
effect for real uses. Including all template parameters means that we
deduce all parameters of A when resolving the call, so when we're in the
constraint we don't need to deduce them again, we can just check whether
the deduction produced the desired result. */
This testcase is an example of why my assumption above was wrong. The effect
of the transformations specified by the standard would be roughly
template <class> struct B_deducible;
template <class BT, int BN> struct B_deducible<B<BT,BN>> { };
template <class BT, class... fTs>
auto fp(BT, fTs...) -> A<BT, sizeof...(fTs)>
requires requires { B_deducible<A<BT,sizeof...(fTs)>>(); };
decltype(fp(0,0)) b(0,0);
which works.
A year ago, Mike Spertus had a partial fix for this; any update on that?
