Re: [Boost-users] class API return a const&, optional, shared_ptr

25 Nov 2008

      Hicham Mouline wrote:
...
hello,
I have a class A that holds a container of objects of type B indexed by int
for e.g.
Typically, I have a function of A
class A {
public:
    const B& getB(int  <index> ) const;
private:
   std::map< int, shared_ptr<B> > listOfBs_;
};
The implementation of getB could be
const B& A::getB(int <index> ) const 
{
    //what to do if index not found
}
A number of solutions I think of:
1. 
boost::optional getB(int <index> ) const 
{
}
2.
change signature to
const B* getB(int <index> ) const
3.
Define a 
static const B notFoundB;
const B& A::getB(int <index> ) const
returns notFoundB when not found and have API users compare return value
with notFoundB
I suppose the cheapest in overhead/performance is 2... optional must have
some  time overhead?
Are there advised solutions? Favourites in terms of style?
Regards,
There's always:

boost::shared_ptr<const B> get(int i) const
{
    ... // find iterator at key i

    return (... != listOfBs.end())
         ? const_pointer_cast<const B>(*non_end_itr)
         : boost::shared_ptr<const B>();
}

or better yet, you can fully encapsulate the internals of A, while 
simplifying the class interface:

void A::visit(int i, boost::function fnc) const
{
    ... // find iterator at key i

    if( ... != listOfBs.end()) f(*non_end_itr);
}

In Joel de Guzman's words: "Don't call us, we'll call you!"

By the way listOfBs is a misleading name.

Jeff

Re: [Boost-users] class API return a const&, optional, shared_ptr

Jeff Flinn