I just discovered that optional<T> is not safe under self-assignment. Consider the following code fragment: boost::optional<long> x(1); //At this point x is initialized and *x == 1 x = x; //x should be unchanged, but instead x is now uninitialized Optional's assignment operator looks like optional& operator= ( optional const& rhs ) { this->assign( rhs ) ; return *this ; } and assign is defined by void assign ( argument_type val ) { destroy(); construct(val); } Thus, if (this == &rhs) in operator=(), any value held by rhs will be destroyed. I can see two possible fixes for this. the first is to put an "if (this != &rhs) " around the call to assign in operator=(). This is simplest, but it slows the code down in order to protect against a very rare situation. The other is to rewrite assign as follows: void assign(argument_type val) { if (m_initialized) { get() = val; // call assignment operator } else { construct(val); //call copy constructor } return *this; } This makes optional self-assignment safe. It has the added advantage that is T's assignment operator has the strong exception safety guarantee, so does optional<T>'s assignment operator. It has the disadvantage of making optional depend on both assignment operator and copy constructor to copy, but very few classes have a copy constructor but don't have an assignment operator. Joe Gottman