Re: A question on "uncopyable" that disable copy constructor

From:

Ian Collins <ian-news@hotmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 29 Feb 2012 11:15:50 +1300

Message-ID:

<9r520mFcg8U6@mid.individual.net>

On 02/29/12 11:02 AM, Jorgen Grahn wrote:

On Tue, 2012-02-28, Ian Collins wrote:

On 02/28/12 09:58 AM, Jorgen Grahn wrote:

I'm also not sure that I'd prefer finding a null pointer in my array,
compared to finding a nil HomeForSale.

Using shared_ptr<T> removes most of those issues.

I think that last issue is enough for me.

   std::Vector<HomeForSale> homes = lots_of_homes();
   assert(!homes.empty());
   const HomeForSale& home = homes[0];
   assert(home.valid());

is not much worse compared to

   std::Vector<shared_ptr<HomeForSale> > homes = lots_of_homes();
   assert(!homes.empty());
   shared_ptr<HomeForSale> home = homes[0];
   assert(home.get());

In both cases I cannot statically know that I can pull a valid home
from the non-empty vector.

You could prevent default initialisation of the pointer:

#include <vector>
#include <tr1/memory>

struct X {};

struct Ptr : std::tr1::shared_ptr<X>
{
   explicit Ptr( X* x ) : std::tr1::shared_ptr<X>(x) {}

private:
   Ptr() {}
};

int main() {
   std::vector<Ptr> v(10);
}

Which is quite handy.

--
Ian Collins