https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66042
Bug ID: 66042
Summary: Implicitly converts lvalue to rvalue when returning
reference parameter in function template
Product: gcc
Version: 5.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: david at doublewise dot net
Target Milestone: ---
#include <type_traits>
template<typename T>
auto compiles(T && t) -> T && {
static_assert(std::is_same<T, int>::value, "Incorrect type deduced for
T.");
return t;
}
static_assert(std::is_same<int &&, decltype(compiles(0))>::value, "shouldn't
compile");
auto fails(int && t) -> int && {
return t;
}
static_assert(std::is_same<int &&, decltype(fails(0))>::value, "doesn't
compile");
Neither function should compile. In the function template case, T is deduced as
int, so the parameter type is int &&. Local variables and function parameters
taken by value can be implicitly moved into the return value, but not function
parameters taken by rvalue reference (t is an lvalue, even though decltype(t)
== int &&).
The non-template function correctly honors this behavior.
If the return type of compiles is changed to decltype(auto) or auto &&, then
the function correctly returns int & and the static_assert fires.
