| Issue |
99845
|
| Summary |
designated initializer of template class rejected by clang
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
Rush10233
|
The following code is rejected by clang but accepted by gcc and MSVC with `-std=c++20`:
```c++
template <typename T>
struct Foo {
T x;
};
template <typename T> auto tst(){
auto foo=Foo{.x=0};
//auto foo=Foo{0};
return foo;
}
int main()
{
auto res=tst<int>();
}
```
It seems that in the instantiation of `foo`, the template argument `T` of `Foo<T>` could be deduced to `int` according to the type of `Foo::x`, while clang complains about the deduction failure of `T`:
```c++
<source>:7:14: error: no viable constructor or deduction guide for deduction of template arguments of 'Foo'
7 | auto foo=Foo{.x=0};
| ^
<source>:14:14: note: in instantiation of function template specialization 'tst<int>' requested here
14 | auto res=tst<int>();
| ^
<source>:2:8: note: candidate template ignored: couldn't infer template argument 'T'
2 | struct Foo {
| ^
<source>:2:8: note: implicit deduction guide declared as 'template <typename T> Foo(int) -> Foo<T>'
<source>:2:8: note: candidate template ignored: could not match 'Foo<T>' against 'int'
<source>:2:8: note: implicit deduction guide declared as 'template <typename T> Foo(Foo<T>) -> Foo<T>'
<source>:2:8: note: candidate function template not viable: requires 0 arguments, but 1 was provided
<source>:2:8: note: implicit deduction guide declared as 'template <typename T> Foo() -> Foo<T>'
1 error generated.
```
It's also worth noting that using `auto foo=Foo{0}` does not trigger any error.
[https://godbolt.org/z/d3ccWsjWa](https://godbolt.org/z/d3ccWsjWa)
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