Destructor running twice on class instance declared inside lambda capture specifier - c++

Question

When running the following code, it seems that the destructor is running twice. I have a theory that this might have to do with an automatic move constructor being added, but I'm not sure how to test this.
#include <iostream>
#include <functional>
struct Structure {
Structure(int n) :
Value(n) {
std::cout << "constructor: " << Value << std::endl;
}
~Structure() {
std::cout << "destructor: " << Value << std::endl;
}
int Value;
};
int main() {
int Init = 4;
std::function<void()> Function = [Instance = Structure(Init)] () {
std::cout << "Value is: " << Instance.Value << std::endl;
};
Function();
Function();
return 0;
}
Output:
constructor: 4
destructor: 4
Value is: 4
Value is: 4
destructor: 4
Is this output correct?

Answer 1

std::function works by copying the callable object you provide. There is no copy-elision here, since your lambda is not an std::function but of an anonymous, unrelated type.
Hence, the two destructors you see are:
The Instance member of the original, temporary, lambda;
The Instance member of the copy of the lambda that was stored into the std::function and lived until the end of main.

Answer 2

Ok, I defined the move and copy constructors manually and also saw errors when I instructed the compiler to delete them in a variant of the code below. Everything seems normal.
Revised code:
#include <iostream>
#include <functional>
struct Structure {
Structure(int n) :
Value(n) {
std::cout << "constructor: " << Value << std::endl;
}
Structure(const Structure& other) :
Value(other.Value) {
std::cout << "copy constructor: " << Value << std::endl;
}
Structure(Structure&& other) :
Value(other.Value) {
other.Value = -1;
std::cout << "move constructor: " << Value << std::endl;
}
~Structure() {
std::cout << "destructor: " << Value << std::endl;
}
int Value;
};
int main() {
int Init = 4;
std::function<void()> Function = [Instance = Structure(Init)] () {
std::cout << "Value is: " << Instance.Value << std::endl;
};
Function();
Function();
return 0;
}
Output:
constructor: 4
move constructor: 4
destructor: -1
Value is: 4
Value is: 4
destructor: 4