On Sun, 5 Aug 2012, John Maddock wrote:
Uh? This is indeed what happens, but for GMP types, unless you added in your wrapper a special 0 state (which you then have to test in every operation), every constructor has to allocate, including the move constructor, since a moved-from object must still be in a valid state.
Did you add an empty state then?
The move constructor doesn't allocate - it takes ownership of the GMP variable, and sets the variable in the moved-from object to a null state. The *destructor* then has an added check to ensure it doesn't try and clear null GMP objects: that's basically the only change. IMO the cost of the extra if statement in the destructor is worth it - and should be trivial compared to calling the external library routine to clear the GMP variable.
Well, what happens then if you do something to a moved-from object other than destructing it? number a=2; number b=move(a); a=2; // or a=b; or a=b+1; or ... -- Marc Glisse