On Jun 22, 2008, at 11:49, Ovanes Markarian wrote:
Does anyone have a suggestion as to how I can get a value out of a boost::any for which I don't know the specific type stored in it? if you know the set of types you operate on consider using boost::variant which supports visitor pattern for dispatching of currently stored type.
Yes, I'll have to look into boost::variant. Thanks for that pointer, all.
Hope that helps. It is difficult to make suggestions, because we don't if you are allowed to modify the interface.
Right. And a very good point to bring up. I am constructing this 100% myself from scratch, so anything *can* be done. The super-class in which I'm trying to extract this value is a generic database access object. The boost::any is being returned from a "get me the value of column X in table Y" method, implemented by any subclass that implements the database-specific layer. So, the values could literally be any value that could be stored in any data value in any database, which is why I was trying to use something very generic. This particular function, the first I'm implementing in the design as I'm building it out, is asking for a value it knows will be effectively boolean. But, depending on the underlying database, may be an int, or some other type. The first case I'm coding is using an sqlite3 subclass of the database object, and there is no boolean type. There is an integer type, and since that database (in current versions) supports 64-bit integers, I've coded that method to return a boost::any<int64_t> when it finds an integer column it's to return. I'm not sure boost::variant is sufficiently flexible given what I want to do, but it clearly bears investigation as I hadn't looked at it yet. I'd be happy to hear any design suggestions from anyone who can think of a good way to do this. I suppose I could make some sort of template class for "database column value", but I'd hoped not to have to do that. - Chris