https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64969
Bug ID: 64969
Summary: generic functions do not work with placeholder return
types
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: rs2740 at gmail dot com
GCC 4.9 added generic functions based on the draft Concepts Lite TS N3889.
(They now called abbreviated function templates.) However, the implementation
does not work with placeholder return types (including both deduced ones and
trailing return types).
For example, all three declarations
auto f1(auto x) { return x++; }
decltype(auto) f2(auto x) { return x++; }
auto f3(auto x) -> int { return x++; }
are apparently treated as if they were equivalent to
template<class T>
T f1(T x) { return x++; }
// etc.
rather than
template<class T>
auto f1(T x) { return x++; }
// etc.
This is easily observable with
struct X {
int operator++(int) const { return 0; }
};
f1(X());
which does not compile, complaining that int cannot be converted to X.
