salsa/examples/selection/util1.rs

use super::*;

// ANCHOR: util1
#[salsa::query_group(Request)]
trait RequestUtil: RequestParser {
    fn content_type(&self) -> Option<String>;
}

fn content_type(db: &dyn RequestUtil) -> Option<String> {
    db.parse()
        .header
        .iter()
        .find(|header| header.key == "content-type")
        .map(|header| header.value.clone())
}
// ANCHOR_END: util1
rework book a little bit - extend some of the empty sections, add a new common pattern - also, show how to use anchors and include so we can test the sources for common patterns 2019-09-24 10:08:30 +00:00			`use super::*;`

			`// ANCHOR: util1`
			`#[salsa::query_group(Request)]`
			`trait RequestUtil: RequestParser {`
			`fn content_type(&self) -> Option<String>;`
			`}`

remove the `DB` parameter This had two unexpected consequences, one unfortunate, one "medium": * All `salsa::Database` must be `'static`. This falls out from `Q::DynDb` not having access to any lifetimes, but also the defaulting rules for `dyn QueryGroup` that make it `dyn QueryGroup + 'static`. We don't really support generic databases anyway yet so this isn't a big deal, and we can add workarounds later (ideally via GATs). * It is now statically impossible to invoke `snapshot` from a query, and so we don't need to test that it panics. This is because the signature of `snapshot` returns a `Snapshot<Self>` and that is not accessible to a `dyn QueryGroup` type. Similarly, invoking `Runtime::snapshot` directly is not possible becaues it is crate-private. So I removed the test. This seems ok, but eventually I would like to expose ways for queries to do parallel execution (matklad and I had talked about a "speculation" primitive for enabling that). * This commit is 99% boilerplate I did with search-and-replace. I also rolled in a few other changes I might have preferred to factor out, most notably removing the `GetQueryTable` plumbing trait in favor of free-methods, but it was awkward to factor them out and get all the generics right (so much simpler in this version). 2020-07-03 10:46:00 +00:00			`fn content_type(db: &dyn RequestUtil) -> Option<String> {`
rework book a little bit - extend some of the empty sections, add a new common pattern - also, show how to use anchors and include so we can test the sources for common patterns 2019-09-24 10:08:30 +00:00			`db.parse()`
			`.header`
			`.iter()`
			`.find(\|header\| header.key == "content-type")`
			`.map(\|header\| header.value.clone())`
			`}`
			`// ANCHOR_END: util1`