David Abrahams wrote:
Jody Hagins <jody-boost-011304@atdesk.com> writes:
It seems to me that implementing the canonical assignment operator would work fine...
optional & operator=(optional const & rhs) { optional tmp(rhs); optional_swap(*this, tmp); return *this; }
I wish people would stop calling it that. It's easy, but it's overkill.
No, it is not overkill. It is the easiest way to implement a correct assignment operator. Forget performance. Subtle bugs in assignment are notoriously hard to find. To give the "canonical" example: optional& operator=( T const & t ) { // destroy and recreate } Consider what happens when an optional holds a tree node and is assigned a child of that node. Or in general, when the 'destroy' step indirectly destroys the right hand side. A correct assignment operator should typically handle self-assignment without an explicit test. Adding the test usually doesn't fix the problem, only its most obvious manifestation. Of course if correctness is not a concern, copy+swap is always overkill.