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RFC: describe in_db functions

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Niko Matsakis 2020-07-05 10:34:15 +00:00
parent fad97eeb6a
commit b59dcc9145
1 changed files with 7 additions and 22 deletions
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29
book/src/rfcs/RFC0006-Dynamic-Databases.md
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@ -165,30 +165,15 @@ combines the `Runtime` (whose type no longer references `DB` directly) with an
type, cannot appear in any public interface, it is just used by the various
implementations that are created by `salsa::database`.
### The query method on `salsa::Database` moves to a helper method
### Instead of `db.query(Q)`, you write `Q.in_db(&db)`
As a consequence of the previous point, the existing `query` and `query_mut`
methods on the `salsa::Database` trait will be moved to an extension trait,
automatically implemented for all salsa databases:
```rust,ignore
pub trait DatabaseExt {
#[allow(unused_variables)]
fn query<Q>(&self, query: Q) -> QueryTable<'_, Self, Q>
where
Q: Query<Self>,
Self: plumbing::GetQueryTable<Q>,
{
<Self as plumbing::GetQueryTable<Q>>::get_query_table(self)
}
fn query_mut<Q>(&mut self, query: Q) -> QueryTableMut<'_, Self, Q> ... { }
}
impl<DB: ?Sized + salsa::Database> DatabaseExt for DB {
...
}
```
methods on the `salsa::Database` trait are changed to methods on the query types
themselves. So instead of `db.query(SomeQuery)`, one would write
`SomeQuery.in_db(&db)` (or `in_db_mut`). This both helps by making the
`salsa::Database` trait dyn-safe and also works better with the new use of `dyn`
types, since it permits a coercion from `&db` to the appropriate `dyn` database
type at the point of call.
### The salsa-event mechanism will move to dynamic dispatch