问Return lambda在常量成员函数中捕获非常量this

EN

#include <functional>
#include <iostream>

using std::cout;
using std::function;
using std::ostream;

namespace abstract {
struct Foo {
    virtual ~Foo() = default;
    virtual auto get_remote_control() const -> function<void()> = 0;
};
} // abstract

namespace concrete {
struct Bar : abstract::Foo {
    int state = 0;
    auto get_remote_control() const -> function<void()> override;
};

static auto operator<<(ostream& out, Bar const& bar) -> ostream& {
    return out << bar.state;
};
} // concrete

int main() {
    concrete::Bar bar;
    abstract::Foo const& foo = bar;
    auto remote_control = foo.get_remote_control();
    cout << "Before, Bar{" << bar << "}\n";
    remote_control();
    cout << "After, Bar{" << bar << "}\n";
}

auto concrete::Bar::get_remote_control() const -> function<void()> {
    return [this]{ Bar& mut_self = *const_cast<Bar*>(this); ++mut_self.state; };
}