https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113242
Bug ID: 113242
Summary: g++ rejects-valid template argument of class type
containing an lvalue reference
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: janschultke at googlemail dot com
Target Milestone: ---
## Code to Reproduce
struct wrapper {
int& ref;
constexpr wrapper(int& ref) : ref(ref) {}
};
template <const wrapper& X>
void fun1() {}
template <wrapper X>
void fun2() {
fun1<X>();
}
int main() {
static int val = 22;
fun2<val>();
}
## Incorrect Output (GCC 14, -std=c++20) (https://godbolt.org/z/1jzqza73z)
<source>: In instantiation of 'void fun2() [with wrapper X = wrapper{val}]':
<source>:16:14: required from here
16 | fun2<val>();
| ~~~~~~~~~^~
<source>:11:12: error: no matching function for call to 'fun1<wrapper{val}>()'
11 | fun1<X>();
| ~~~~~~~^~
<source>:7:6: note: candidate: 'template<const wrapper& X> void fun1()'
7 | void fun1() {}
| ^~~~
<source>:7:6: note: template argument deduction/substitution failed:
<source>:11:12: error: the address of 'wrapper{val}' is not a valid template
argument
11 | fun1<X>();
| ~~~~~~~^~
## Explanation
None. Clang compiles this, but GCC doesn't. The reference contained within
wrapper is a valid template argument (see
https://eel.is/c++draft/temp.arg.nontype#6), but falsely disqualifies X in fun1
from binding to X in fun2.
See https://stackoverflow.com/a/77764351/5740428 for a more detailed
explanation for the relevant standardese.
