Re: Classes that manage containers

From:
Pete Becker <pete@versatilecoding.com>
Newsgroups:
comp.lang.c++.moderated
Date:
Mon, 9 Jul 2012 16:03:34 -0700 (PDT)
Message-ID:
<2012070915351471622-pete@versatilecodingcom>
On 2012-07-09 15:31:15 +0000, fmatthew5876 said:

Lets say we have something like this:
class A {
 public:
   //Stuff..
 private:
   SomeContainer<B> _bcontainer;
}
We want A to contain the storage for a collection of B's and we want to
allow the user to add/remove and do other operations to B through A.
One option is to add class methods to A to manipulate B such as:
void A::bcontainer_insert(int i, const T& t) { _bcontainer.insert(i, t); }
This is simple and it also allows us to restrict the interface (for
example only provide stack-like push/pop methods even though the
underlying container is an array) to B but it can get unwieldy. In
most cases the names of the methods all have to contain a prefix
or suffix saying they deal with the b container. It gets even more
messy if our A class manages multiple containers of different objects.
Another choice is to just have a method that returns a
reference to the B container.
Container<B>& A::get_b() { return _bcontainer; }
Now all of the b container methods are scoped within the b
container class which seems cleaner. If we want to restrict the
interface we can do it easily using containment.
class BContainer {
 public:
   //Restricted inline interface
 private:
   Container<B> _base;
};
class A {
 public:
   BContainer& get_b() { return _bcontainer; }
   //Stuff..
 private:
   BContainer _bcontainer;
}
It is probably a good idea at this point to make sure
copy constructors are disabled on BContainer so
users can't accidentally do this:
A a;
BContainer bc = a.get_b();
bc.insert(int i, something);
What idiom do you all prefer to use in these situations?


The idiom I prefer is knowing what a class is supposed to do before writing its interface. There's nothing in this post that says anything about the reason that A exists, unless it's just a blob that holds a bunch of containers, in which case it is probably a design mistake, and definitely highly uninteresting.

--
Pete

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