| |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| |
This is a rather tricky piece of functionality. It works as
follows.
We introduce a `CastTable` type. Each `CastTable` tells us how to
downcast `dyn Object` for objects of a single concrete type.
The `Object` type now has a `get_casttable` method that returns
an empty `CastTable` by default.
`CastTable` is, internally, a map from the `TypeId` of the target
dyn Trait reference type to a function
`fn(&dyn Object) -> &dyn Trait`. These functions are stored as
`Box<dyn Any + ...>`. (They are Boxed because they may refer to
generic functions, which you can't get a static reference to,
and they're Any because the functions have different types.)
The `decl_object!` macro now implements `get_casttable` as
appropriate. (The syntax is a bit janky, but that's what we get
for not using derive_adhoc.) For non-generic types, `get_casttable`
uses a Lazy<CastTable>`. to initialize a CastTable exactly once.
For generic types, it use a `Lazy<RwLock<HashMap<..>>` to
build one CastTable per instantiation of the generic type.
This could probably be optimized a bit more, the yaks could be
shaved in a more scintillating hairstyle, and the syntax for
generic `decl_object` could definitely be improved.
|
