Can I safely point to the data of a reassigned boost::optional?

Question

Given the following code sample:

boost::optional< int > opt;
opt = 12;
int* p( &*opt );
opt = 24;
assert( p == &*opt );

Is there any guarantee that the assert will always be valid?

Answer 1

yes it's a guarantee. The T of a boost::optional<T> is a logically a private member of the optional.

the code above is logically equivalent to:

bool opt_constructed = false;
int opt_i; // not constructed

new int (&opt_i)(12); opt_constructed = true; // in-place constructed

int*p = &opt_i;

opt_i = 24;

assert(p == &opt_i);

// destuctor
if (opt_constructed) {
  // call opt_i's destructor if it has one
}