Re: Heterogeneous collection: return type overload

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 18 Feb 2010 12:04:14 -0800 (PST)

Message-ID:

<7a7cc532-8c53-4643-a353-78da7661f161@d2g2000yqa.googlegroups.com>

On Feb 18, 6:50 am, jrbcast <jrbc...@gmail.com> wrote:

On Feb 17, 7:59 pm, "Leigh Johnston" <le...@i42.co.uk> wrote:

"jrbcast" <jrbc...@gmail.com> wrote in message

news:ae30bbcc-2fea-413d-9696-ad036be5d29d@f15g2000yqe.googlegroups.com...

Imagine I have something like this:

class Collection
{
std::map<char *, void *> elements;

Using a char* as a key in a map is probably not a very good
idea.

Collection();

Try "std::map<std::string, boost::any> elements;" instead.

Thanks for your responses. Now it is clear that C++ does not
support function overloading on return types :-(.

Not directly, but it's fairly simple to get the same effect by
means of a proxy:

    class Collection
    {
    public:
        class Proxy
        {
            Collection const* owner;
            std::string key;
        public:
            Proxy(Collection const& owner, std::string const& key)
                : owner(&owner)
                , key(key)
            {
            }
            template< typename T > operator T() const
            {
                return owner->... // whatever it takes to get
                                   // the correctly typed value
            }
        }
        Proxy get(std::string const& key) const
        {
            return Proxy(*this, key);
        }
        // ...
    };

--
James Kanze