Suppose that I have
- three classes
P,C1,C2, - composition (strong aggregation) relations between
P <>- C1andP <>- C2, i.e. every instance ofPcontains an instance ofC1and an instance ofC2, which are destroyed when the parentPinstance is destroyed. - an association relation between instances of
C1andC2(not necessarily between children of the sameP).
To implement this, in C++ I normally
- define three classes
P,C1,C2, - define two member variables of
Pof typeboost::shared_ptr<C1>,boost::shared_ptr<C2>, and initialize them with newly created objects inP‘s constructor, - implement the relation between
C1andC2using aboost::weak_ptr<C2>member variable inC1and aboost::weak_ptr<C1>member variable inC2that can be set later via appropriate methods, when the relation is established.
Now, I also would like to have a link from each C1 and C2 object to its P parent object. What is a good way to implement this?
My current idea is to use a simple constant raw pointer (P * const) that is set from the constructor of P (which, in turn, calls the constructors of C1 and C2), i.e. something like:
class C1
{
public:
C1(P * const p, ...)
: paren(p)
{
...
}
private:
P * const parent;
...
};
class P
{
public:
P(...)
: childC1(new C1(this, ...))
...
{
...
}
private:
boost::shared_ptr<C1> childC1;
...
};
Honestly I see no risk in using a private constant raw pointer in this way but I know that raw pointers are often frowned upon in C++ so I was wondering if there is an alternative solution.
Pointers create headaches when you use them to manage dynamically allocated resources. In this case, however, a pointer is a simple “backlink” to the parent, and it cannot be changed during the lifetime of a child object (i.e. there’s no re-parenting). This is a good solution that helps you keep things simple.
4