Re: const std::map reference and __declspec property

From:

"Heinz Ozwirk" <hozwirk.SPAM@arcor.de>

Newsgroups:

microsoft.public.vc.language

Date:

Mon, 17 Jul 2006 08:14:37 +0200

Message-ID:

<44bb2acf$0$10513$9b4e6d93@newsread4.arcor-online.net>

"Carl Daniel [VC++ MVP]" <cpdaniel_remove_this_and_nospam@mvps.org.nospam>
schrieb im Newsbeitrag news:e3BW7RVqGHA.4608@TK2MSFTNGP04.phx.gbl...

matthew breedlove wrote:

Is there any container class better suited to this that has an
operator[] that can be used on a const version of the object?
Alternatively, is there a better way to go about accomplishing this?

I can't think of anything in the standard library that would help.
Rather, I'd suggest writing a wrapper class that exposes the desired parts
of the std::map interface in a const-friendly way, and exposing that type
as your property type instead of the map itself. If operator[] is all you
need on the property, this wrapper type should be only a few lines of
code.

If operator[] is all that is needed, the subscript can as well be used with
the property itself:

    std::map<KeyType, ValueType> theMap;
    __declspec(property(get=get_Element)) ValueType const& Element[];
    ValueType const& get_Element(KeyType const& key) const
    {
        std::map<...>::const iterator it = theMap.find(key);
        if (it == theMap.end()) throw std::out_of_range(...);
        return it->second;
    }

No need for a wrapper in this simple case.

HTH
    Heinz