gcc bug source gccbug.cpp

#include <type_traits>
#include <iostream>

template<typename T, typename Param>
concept bool UnaryFunction = requires(const T& func) {
    func(std::declval<Param>());
};

template<typename IT, typename Func>
requires UnaryFunction<Func, decltype(*std::declval<IT>())>
Func for_each(IT first, IT last, Func func)
{
    for(auto it = first; it != last; ++it) {
        func(*it);
    }
    return func;
}

int main() {
    auto numbers = { 1, 2, 3, 4, 5 };
    std::cout << "numbers:\n";

    // gcc 7.2 segfaulted for some reason at the next statement
    for_each(numbers.begin(), numbers.end(), [](auto n) {
        std::cout << n << '\n';
    });
}