That would require me to declare up front which types were usable and which weren't. I'm looking for a solution where I don't need to do that; that is, allow me to add new components to the system with new configuration parameter types, without having to go to a central source location and declare these types there.
On Fri, Aug 23, 2013 at 7:54 AM, Abhijeet Gaiha <[email protected]>wrote: > You could define an enum that encapsulates all known types. > > enum monster { > Integer(int), > Float(float), > .... > } > > Then use a container for this type. > On Aug 23, 2013 10:20 AM, "Oren Ben-Kiki" <[email protected]> wrote: > >> Is it possible to implement something like Haskell's Dynamic value holder >> in Rust? (This would be similar to supporting C++'s dynamic_cast). >> Basically, something like this: >> >> pub struct Dynamic { ... } >> impl Dynamic { >> pub fn put(value: ~T) { ... } >> pub fn get() -> Option<T> { ... } >> } >> >> I guess this would require unsafe code... even so, it seems to me that >> Rust pointers don't carry sufficient meta-data for the above to work. A >> possible workaround would be something like: >> >> pub struct Dynamic { type_name: ~str, ... } >> impl Dynamic { >> pub fn put(type_name: &str, value: ~T) { Dynamic { type_name: >> type_name, ... } } >> pub fn get(&'a self, type_name: &str) -> Option<&'a T> { >> assert_eq!(type_name, self.type_name); ... } } >> } >> >> And placing the burden on the caller to always use the type name "int" >> when putting or getting `int` values, etc. This would still require some >> sort of unsafe code to cast the `~T` pointer into something and back, while >> ensuring that the storage for the `T` (whatever its size is) is not >> released until the `Dynamic` itself is. >> >> (Why do I need such a monstrosity? Well, I need it to define a >> `Configuration` container, which holds key/value pairs where whoever sets a >> value knows its type, whoever gets the value should ask for the same type, >> and the configuration can hold values of "any" type - not from a predefined >> list of types). >> >> Is such a thing possible, and if so, how? >> >> Thanks, >> >> Oren Ben-Kiki >> >> _______________________________________________ >> Rust-dev mailing list >> [email protected] >> https://mail.mozilla.org/listinfo/rust-dev >> >>
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