| Summary: | [concepts] multidimensional subscript operator inside requires with variable template arguments is broken | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Luke Dalessandro <ldalessandro> |
| Component: | c++ | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED DUPLICATE | ||
| Severity: | normal | CC: | ppalka, webrown.cpp |
| Priority: | P3 | Keywords: | rejects-valid |
| Version: | 13.0 | ||
| Target Milestone: | --- | ||
| See Also: | https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102611 | ||
| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | Last reconfirmed: | 2023-02-09 00:00:00 | |
| Bug Depends on: | |||
| Bug Blocks: | 67491 | ||
Confirmed, even this is rejected:
```
auto foo(auto a, auto... i) -> decltype(auto) {
if constexpr (requires { a[i...]; }) {
return a[i...];
}
else {
return a;
}
}
int x = foo(1, 1);
```
Note clang just ICEs.
Also the above works if it is not a variable argument auto ...
That is:
```
template<typename T, typename T1>
auto foo(T a, T1 i) {
if constexpr (requires { a[i]; }) {
return a[i];
}
else {
return a;
}
}
int x = foo(1, 1);
```
Compiles just fine.
dup of the recently fixed PR111493 *** This bug has been marked as a duplicate of bug 111493 *** |
The following code produces an error when evaluating the concept. auto foo(auto a, auto... i) -> decltype(auto) { if constexpr (requires { a[i...]; }) { return a[i...]; } else { return a; } } int x = foo(1); > <source>: In instantiation of 'decltype(auto) foo(auto:1, auto:2 ...) [with auto:1 = int; auto:2 = {}]': > <source>:10:12: required from here > <source>:2:31: error: built-in subscript operator without expression list > 2 | if constexpr (requires { a[i...]; }) { > | ~^ > Compiler returned: 1 Workaround: specialize on sizeof...(i) to avoid this test when i... is empty. Live example: https://godbolt.org/z/K3oezd1qz