| Issue |
76837
|
| Summary |
Cannot directly call conversion operator in SFINAE context
|
| Labels |
|
| Assignees |
|
| Reporter |
gracicot
|
Clang seem to not expand the template parameter when directly calling a conversion operator in SFINAE context.
Reproduction:
```c++
struct a {
operator int();
};
template<typename A>
struct b {
template<typename B, decltype(void(A{}.operator B()))* = nullptr>
auto func() {}
};
int main() {
b<a>{}.func<int>();
}
```
GCC and clang compile this code correctly, clang fails with:
```
<source>:7:40: error: no member named 'operator type-parameter-0-0' in 'a'
7 | template<typename B, decltype(void(A{}.operator B()))* = nullptr>
| ~~~ ^
<source>:12:5: note: in instantiation of template class 'b<a>' requested here
12 | b<a>{}.func<int>();
| ^
<source>:12:12: error: no member named 'func' in 'b<a>'
12 | b<a>{}.func<int>();
| ~~~~~~ ^
<source>:12:20: error: expected '(' for function-style cast or type construction
12 | b<a>{}.func<int>();
| ~~~^
<source>:12:22: error: expected _expression_
12 | b<a>{}.func<int>();
| ^
4 errors generated.
```
Compiler explorer link: https://godbolt.org/z/6on57GehY
This seems to only happen when the template parameter is not immediate context. Defining `struct b` as follows will make clang accept the code:
```
struct a {
operator int();
};
struct b {
template<typename A, typename B, decltype(void(A{}.operator B()))* = nullptr>
auto func() {}
};
int main() {
b{}.func<a, int>();
}
```
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