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Question #319 Difficulty: 2

According to the C++23 standard, what is the output of this program? 

    #include <iostream>

struct A {
    A() { std::cout << "a"; }

    void foo() { std::cout << "1"; }
};

struct B {
    B() { std::cout << "b"; }
    B(const A&) { std::cout << "B"; }

    void foo() { std::cout << "2"; }
};

int main()
{
    auto L = [](auto flag) -> auto {return flag ? A{} : B{};};
    L(true).foo();
    L(false).foo();
}

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