https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86703
Bug ID: 86703
Summary: template auto fails deduction, where template int
succeeds
Product: gcc
Version: 7.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: barry.revzin at gmail dot com
Target Milestone: ---
Reduced example from https://stackoverflow.com/q/51561232/2069064:
struct false_type {
static constexpr bool value = false;
};
template <AUTO> // (*) -DAUTO=auto or -DAUTO=int
struct true_type {
static constexpr bool value = true;
};
template <class T>
true_type<(T::value(), void(), 0)> match_auto(int);
template <class>
false_type match_auto(...);
struct pass {
static constexpr int value() { return 1; }
};
struct fail { };
static_assert(decltype(match_auto<pass>(0))::value);
static_assert(!decltype(match_auto<fail>(0))::value);
With -DAUTO=int, this compiles. With -DAUTO=auto, the first static_assert (on
pass) triggers (on gcc 7.3, 8.1, and trunk). There shouldn't be a difference
here between int and auto. Both forms compile on clang.
