object-lifetime

I understand that if a temporary is bound to a reference member in the constructor's initializer list, the object will be destroyed as the constructor returns. However , consider the following code: #include <functional> #include <iostream> using callback_func = std::function<int(void)>; int func(const callback_func& callback) { struct wrapper { const callback_func& w_cb; wrapper(const callback_func& cb) : w_cb {cb} { } int call() { return this->w_cb() + this->w_cb(); } }; wrapper wrp {callback}; return wrp.call(); } int main() { std::cout << func([](){ return 21; }) << std::endl; return 0; }

I don't understand this: 3.8/1 "The lifetime of an object of type T ends when: — if T is a class type with a non-trivial destructor (12.4), the destructor call starts , or — the storage which the object occupies is reused or released." If the lifetime ends before the destructor starts, doesn't that mean accessing members in the destructor is undefined behavior? I saw this quote too: 12.7 "For an object with a non-trivial destructor, referring to any non-static member or base class of the object after the destructor finishes execution results in undefined behavior." But it doesn't make clear

Suppose I have a code as follows: int Main() { if (true) { new Thread(()=> { doSomeLengthyOperation(); }).Start(); } while (true) { //do nothing } } There are 2 threads, I'm going to call the Main thread the thread that is executing the Main() function, and the thread being new'ed up inside the "if" test as Thread A. My question is, when does Thread A get destroyed? Will doSomeLenghtyOperation() be able to run into completion? Since there are no references pointing at Thread A, will it be marked as a candidate for garbage collection: Immediately after the "new Thread().Start()" statement