| Issue |
98963
|
| Summary |
lambda in class body should have the same type among different TUs
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
namniav
|
[basic.def.odr#15.6](https://eel.is/c++draft/basic.def.odr#15.6)
> In each such definition, except within the default arguments and default template arguments of `D`, corresponding *lambda-_expression_*s shall have the same closure type
When the lambda _expression_ is used with `decltype` in side class body(but not inside a function), Clang with libc++ generates different closure types in different TUs.
Clang with libstdc++ seems not have this problem. GCC also has this problem for both `F1` and `F2`.
Demo: https://godbolt.org/z/M4xjWesYn
* common.hpp
```c++
#include <typeinfo>
#include <array>
struct A {
using F1 = decltype([]{}); // Clang with libc++ generates different closure types for different TUs
inline static auto f2 = []{};
using F2 = decltype(f2); // Clang Ok, GCC No
};
[[gnu::always_inline]]
inline auto func() {
using F3 = decltype([]{}); // OK
auto f4 = []{};
using F4 = decltype(f4); // OK
return std::array{ &typeid(F3), &typeid(F4) };
}
auto FOOBAR() {
auto t = func();
return std::array{
&typeid(A::F1),
&typeid(A::F2),
t[0],
t[1]
};
}
```
* foo.cpp
```c++
#define FOOBAR foo
#include "common.hpp"
```
* bar.cpp
```c++
#define FOOBAR bar
#include "common.hpp"
```
* main.cpp
```c++
#include <cstdio>
#include <typeinfo>
#include <array>
std::array<const std::type_info*, 4> foo();
std::array<const std::type_info*, 4> bar();
int main() {
auto f = foo();
auto b = bar();
for (int i = 0; i < 4; ++i) {
std::printf("F%d same type ? %d\n", i+1, *f[i] == *b[i]);
//std::printf("name=%s hash_code=%-20llu addr=%p\n", f[i]->name(), (unsigned long long)f[i]->hash_code(), f[i]);
//std::printf("name=%s hash_code=%-20llu addr=%p\n", b[i]->name(), (unsigned long long)b[i]->hash_code(), b[i]);
}
}
```
**Outputs** :
* Clang, libc++
> ```
> F1 same type ? 0
> F2 same type ? 1
> F3 same type ? 1
> F4 same type ? 1
> ```
* Clang, libstdc++
> ```
> F1 same type ? 1
> F2 same type ? 1
> F3 same type ? 1
> F4 same type ? 1
> ```
* GCC, libstdc++
> ```
> F1 same type ? 0
> F2 same type ? 0
> F3 same type ? 1
> F4 same type ? 1
> ```
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