auto return type

auto.cpp

#include <optional>
#include <iostream>


auto foo(int x)
{
    if (x > 5)
        return std::optional<int>{x};
    else
        return std::nullopt;
}

int main()
{
    std::cout << foo(3).has_value() << ' ' << foo(7).has_value() << std::endl;
    return 0;
}

output

~
❯ g++ autohell.cpp
autohell.cpp: In function ‘auto foo(int)’:
autohell.cpp:10:21: error: inconsistent deduction for auto return type: ‘std::optional<int>’ and then ‘std::nullopt_t’
   10 |         return std::nullopt;
      |                ~~~~~^~~~~~~