| Issue |
126246
|
| Summary |
tuple variant crashing iterating over vector with std::apply (clang 17.0.1 - clang 19.1.0)
|
| Labels |
clang
|
| Assignees |
|
| Reporter |
wh1t3lord
|
## Problem
Here's a function that fills a std::vector<std::variant<Ts...>> from a std::vector<std::string_view>. The function template takes a std::tuple<Ts...> as a type parameter and uses std::apply to iterate over the tuple's types. It attempts to convert each string in the input vector to the corresponding type or keeps it as a string if conversion is not possible.
## Code & Proof
```cpp
#include <iostream>
#include <vector>
#include <variant>
#include <tuple>
#include <string_view>
#include <cstdlib> // for std::atoi, std::atof
#include <type_traits>
template <typename... Ts>
std::vector<std::variant<Ts...>> fill_vector(const std::vector<std::string_view>& input) {
using VariantType = std::variant<Ts...>;
std::vector<VariantType> result;
result.reserve(input.size());
for (const auto& str : input) {
bool converted = false;
// Create a temporary tuple to pass to std::apply
std::tuple<Ts...> tempTuple;
std::apply([&](auto&&... args) {
// Fold _expression_ to try each type
(([&] {
using T = std::decay_t<decltype(args)>;
if (!converted) {
if constexpr (std::is_integral_v<T>) {
try {
result.emplace_back(static_cast<T>(std::atoi(str.data())));
converted = true;
} catch (...) {}
} else if constexpr (std::is_floating_point_v<T>) {
try {
result.emplace_back(static_cast<T>(std::atof(str.data())));
converted = true;
} catch (...) {}
}
}
}()), ...);
}, tempTuple);
if (!converted) {
result.emplace_back(std::string(str)); // Fallback to string
}
}
return result;
}
int main() {
std::vector<std::string_view> input = {"123", "45.67", "hello", "789"};
auto output = fill_vector<int, double, std::string>(input);
for (const auto& v : output) {
std::visit([](const auto& value) { std::cout << value << " "; }, v);
}
return 0;
}
```
Proof №1: https://godbolt.org/z/TPv4vcGch (clang 17.0.1)
Proof №2: https://godbolt.org/z/178zP4x9v (clang 19.1.0)
So both crashes.
### Working sample (Expected behaviour)
Unexpected but it compiles on gcc.
Link: https://godbolt.org/z/W8jqWqzE3 (gcc 12.1)
Link: https://godbolt.org/z/n9GWG4EM8 (gcc 14.2)
## Crash backtrace
Proceed to godbolt site with attached link in previous section.
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