https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90210
Bug ID: 90210
Summary: [C++17] CTAD forbidding explicit deduction guide for
copy-list-initialization
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: tyker at outlook dot com
Target Milestone: ---
gcc currently allows the following code:
template<typename T> struct tuple { tuple(T); };
template<typename T> explicit tuple(T t) -> tuple<T>;
tuple t = { 1 };
this should fail to compile because the deduction guide is marked explicit.
the issue may come from the implicit deduction guide not being overridden by
the user defined one.
example from other compilers:
https://godbolt.org/z/M198L5
the standard says in [over.match.list]:
"In copy-list-initialization, if an explicit constructor is chosen, the
initialization is ill-formed."
