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" <o...@ben-kiki.org> 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
>
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>
>
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