复制捕获移动对象的lambda

为什么会这样 code snippet 不编译?

#include <functional>
#include <iostream>
#include <memory>

int main()
{
    std::unique_ptr<int> uniq_ptr(new int{6});
    auto foo_a = [&uniq_ptr]{std::cout << *uniq_ptr << std::endl;};
    std::bind(foo_a)(); //works
    foo_a();            //works

    auto foo_b = [up = std::move(uniq_ptr)]()mutable{*up = 5; std::cout << *up << std::endl;};
    foo_b();           //works;

#ifdef CHOOSE_1
    auto foo_b1 = foo_b; //Surprised!  I think `up` could be copied.But the compiler complains: Error: use of deleted function 'main()::<lambda()>::<lambda>(const main()::<lambda()>&)'
#else
    std::bind(foo_b);    //Same error!
#endif
}

对于 auto foo_b = [up = std::move(uniq_ptr)]()mutable{//...} 我想 foo_b 可以复制自 up 一个右值,它可以被move构造函数复制。