| Issue |
171630
|
| Summary |
[ C++ 23] Confusing behavior when temporaries are provided to a function that is part of a range loop initializer.
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
yeongasm
|
https://godbolt.org/z/TT8xM4eYe
When providing temporaries into a function that is used as the for-range-initializer, the temporaries are destroyed before the end of the full _expression_. Sample code can be found below with a live example in compiler explorer. This only happens when the function arguments for `foo` are values. When the function arguments of `foo` are references (l-value / r-value), clang's output matches the one from gcc below.
```cpp
struct Foo
{
int num = 0;
Foo() { std::cout << "Constructed!\n"; }
~Foo() { std::cout << "Destructed!\n"; }
Foo(const Foo&) = default;
Foo(Foo&&) = default;
auto operator=(const Foo&) -> Foo& = default;
auto operator=(Foo&&) -> Foo& = default;
};
struct JankStringView : std::string_view
{
using super = std::string_view;
using super::super;
~JankStringView() { std::cout << "string view is destroyed\n"; }
};
struct JankString : std::string
{
using super = std::string;
using super::super;
~JankString() { std::cout << "string is destroyed\n"; }
};
auto foo([[maybe_unused]] Foo f, [[maybe_unused]] JankStringView view) -> std::vector<int>
{
std::cout << view.data() << "\n";
std::cout << "Exiting coroutine\n";
return { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
};
auto main() -> int
{
for (auto x : foo(Foo{}, JankStringView{ JankString{ "Hello" }.c_str() }))
{
std::cout << "x: " << x << "\n";
}
return 0;
}
```
On Clang (trunk), the output is:
```
Constructed!
Hello
Exiting coroutine
string view is destroyed
Destructed!
x: 1
x: 2
x: 3
x: 4
x: 5
x: 6
x: 7
x: 8
x: 9
x: 10
string is destroyed
```
On GCC (trunk) however, the output is more aligned with the wording that's in the [standard](https://eel.is/c++draft/class.temporary#4).
```
Constructed!
Hello
Exiting coroutine
x: 1
x: 2
x: 3
x: 4
x: 5
x: 6
x: 7
x: 8
x: 9
x: 10
string view is destroyed
string is destroyed
Destructed!
```
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