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104 lines
3.8 KiB
Rust
104 lines
3.8 KiB
Rust
use salsa::Database;
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use std::sync::Arc;
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///////////////////////////////////////////////////////////////////////////
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// Step 1. Define the query group
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// A **query group** is a collection of queries (both inputs and
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// functions) that are defined in one particular spot. Each query group
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// represents some subset of the full set of queries you will use in your
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// application. Query groups can also depend on one another: so you might
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// have some basic query group A and then another query group B that uses
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// the queries from A and adds a few more. (These relationships must form
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// a DAG at present, but that is due to Rust's restrictions around
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// supertraits, which are likely to be lifted.)
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salsa::query_group! {
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trait HelloWorldDatabase: salsa::Database {
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// For each query, we give the name, input type (here, `()`)
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// and the output type `Arc<String>`. Inside the "fn body" we
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// give some other configuration.
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fn input_string(key: ()) -> Arc<String> {
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// The type we will generate to represent this query.
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type InputString;
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// Specify the queries' "storage" -- in this case, this is
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// an *input query*, which means that its value changes
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// only when it is explicitly *set* (see the `main`
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// function below).
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storage input;
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}
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// This is a *derived query*, meaning its value is specified by
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// a function (see Step 2, below).
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fn length(key: ()) -> usize {
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type Length;
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// No explicit storage defaults to `storage memoized;`
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//
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// The function that defines this query is (by default) a
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// function with the same name as the query in the
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// containing module (e.g., `length`).
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}
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}
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}
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///////////////////////////////////////////////////////////////////////////
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// Step 2. Define the queries.
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// Define the **function** for the `length` query. This function will
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// be called whenever the query's value must be recomputed. After it
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// is called once, its result is typically memoized, unless we think
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// that one of the inputs may have changed. Its first argument (`db`)
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// is the "database", which is the type that contains the storage for
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// all of the queries in the system -- we never know the concrete type
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// here, we only know the subset of methods we care about (defined by
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// the `HelloWorldDatabase` trait we specified above).
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fn length(db: &impl HelloWorldDatabase, (): ()) -> usize {
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// Read the input string:
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let input_string = db.input_string(());
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// Return its length:
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input_string.len()
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}
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///////////////////////////////////////////////////////////////////////////
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// Step 3. Define the database struct
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// Define the actual database struct. This must contain a salsa
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// runtime but can also contain anything else you need.
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#[derive(Default)]
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struct DatabaseStruct {
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runtime: salsa::Runtime<DatabaseStruct>,
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}
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// Tell salsa where to find the runtime in your context.
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impl salsa::Database for DatabaseStruct {
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fn salsa_runtime(&self) -> &salsa::Runtime<DatabaseStruct> {
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&self.runtime
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}
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}
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// Define the full set of queries that your context needs. This would
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// in general combine (and implement) all the database traits in
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// your application into one place, allocating storage for all of
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// them.
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salsa::database_storage! {
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struct DatabaseStorage for DatabaseStruct {
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impl HelloWorldDatabase {
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fn input_string() for InputString;
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fn length() for Length;
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}
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}
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}
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// This shows how to use a query.
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fn main() {
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let mut db = DatabaseStruct::default();
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println!("Initially, the length is {}.", db.length(()));
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db.query_mut(InputString)
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.set((), Arc::new(format!("Hello, world")));
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println!("Now, the length is {}.", db.length(()));
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}
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