Re: Problems mixing boost::lambda::bind and boost::shared_ptr..

From:

"Jeff Flinn" <NONONE@nowhere.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 1 Jun 2006 17:01:51 -0400

Message-ID:

<e5nki3$j7v$1@bluegill.adi.com>

See inline response

Toby Bradshaw wrote:

Hi,

Consider the following:

class A
{
public:
  virtual bool foo() = 0;
};

class B : public A
{
public:
  virtual bool foo() { return false; }
};

void fn()
{
  std::list< A * > aList(10);
  std::list< boost::shared_ptr<A> > aSharedList(10);

  // This works fine..
  std::count_if(
    aList.begin(),
    aList.end(),
    boost::lambda::bind(A::foo, boost::lambda::_1)

boost::lambda::bind(&A::foo, boost::lambda::_1)

  );

  // This doesn't compile..
  std::count_if(
    aSharedList.begin(),
    aSharedList.end(),
    boost::lambda::bind(A::foo, boost::lambda::_1)

boost::lambda::bind(&A::foo, boost::lambda::_1)

);
}

--

Why doesn't the second case compile ? The only difference is that I'm
making the call through a shared_ptr instead of a naked one. If
shared_ptr semantics are (essentially) identical to the naked pointer
ones then this should surely work ? Is there some extra syntax
required in the shared_ptr case or does this simply not work ?

I haven't used lambda bind a lot, but boost bind requires the & as shown
above, although some compilers will let you get by without it. Other than
that, the code will result in undefined behaviour since your containers are
not pointing to valid instances.

Jeff Flinn