| Issue |
165734
|
| Summary |
Qualified name lookup using a type pack is not considered a pack
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
MitalAshok
|
Consider the following program:
```c++
struct X {
int i;
};
struct Y {
int i;
};
struct Z : X, Y {};
void g(int, int);
template<class... Bases, class T>
void f(T z) {
g(z.Bases::i...);
}
int main() {
f<X, Y>(Z{});
}
```
Currently Clang complains:
```
<source>:13:17: error: pack expansion does not contain any unexpanded parameter packs
13 | g(z.Bases::i...);
| ~~~~~~~~~~^
```
GCC and MSVC compile this to call `g(0, 0)`.
Clang *does* accept it if `z` is not dependently typed:
```c++
template<class... Bases>
void f(Z z) {
g(z.Bases::i...);
}
```
[[basic.lookup.qual.general]p3](https://wg21.link/basic.lookup.qual.general#3) is pertinent. It appears there is a situation where an _expression_ is dependently a pack based on a template parameter, so this might be a standard defect.
For example, GCC currently accepts:
```c++
struct X {
int i;
};
struct Y {
int i;
};
struct A : X, Y {
using Bases = void;
};
void g(int, int);
template<class... Bases, class T>
void f(T z) { // GCC no longer accepts with non-dependent z `template<class... Bases> void f(Z z) {`
g(z.Bases::i...);
}
int main() {
f<X, Y>(A{});
}
```
But MSVC doesn't accept this, failing when trying to instantiate `f<X, Y>(A{})`.
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