21.01.2013 23:37, Andrey Semashev пишет:
On January 21, 2013 11:27:36 PM Sergey Cheban <s.cheban@drweb.com> wrote:
II: Set operand.p_ to NULL, add BOOST_ASSERT in get operations + good performance + provides noexcept guarantee for move constructor + optimization will be used even if varinat has no type with trivial default constructor + easy to implement - triggers an assert when user tries to reuse moved object - adds an empty state to the recursive_wrapper Let's think about non-recursive variants. For example:
// both CFileObj and CDatabaseObj are movable, not copyable and // not nothrow-default-constructible boost::variant< CFileObj, CDatabaseObj > v1( CFileObj(SomeFileName) ); boost::variant< CFileObj, CDatabaseObj > v2( std::move( v1 ) );
// What would be the state of v1 at this point?
Moved-from CFileObj, I presume. Got it. So, the reasonable and consistent value for the moved-from variant<recursive_wrapper,int> is a moved-from recursive_wrapper, right? In many cases, the moved-from state of the variables is equal to the default-constructed state but this rule is not obligatory.
So, I think that NULL is a valid state of the moved-from recursive_wrapper and the 2nd proposal is not worse (at least) than the 3rd one. -- Best regards, Sergey Cheban