| Issue |
125913
|
| Summary |
Alias template CTAD is erroneously allowed in C++17 mode
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
PJBoy
|
Alias template CTAD is a C++20 feature ( https://en.cppreference.com/w/cpp/compiler_support/20#cpp_deduction_guides_201907L ) recently introduced in clang v19. Seems it's being allowed in C++17 mode with no diagnostic ( https://godbolt.org/z/x7zdxnrqx ). Though a (almost correct) diagnostic is issued with the `-Wpre-c++17-compat` flag ( https://godbolt.org/z/acKsG3dfj ).
Testcase is replicated here
```
template<typename T, typename TT>
struct S
{
T t;
TT tt;
};
template<typename T, typename TT>
S(T, TT) -> S<T, TT>;
template<typename T>
using S_int = S<T, int>;
int main()
{
(void) S_int{1, 2};
}
```
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