A library for ergonomic, performant, incremental computation between arbitrary types.
Most applications rely on some core logic which must respond to external events. Often, the logic to transform each event in to an action is straightforward, but as the application scales, many hard to reason-with situations emerge from the combinatorial explosion of states.
Dependency graphs are an excellent code architecture to tame complexity in such scenarios.
``` rust use std::{collections::HashSet, hash::Hash, sync::Arc};
use depends::{ core::{Depends, Resolve, UpdateDependee, UpdateLeaf}, derives::{Dependee, dependencies, Leaf}, };
// A Leaf is a node which takes new values from outside the graph. Nodes must
// implement Hash, attribute a hashable field as #[depends(hash)] or specify
// #[depends(unhashable)].
pub struct NumberInput { value: i32, }
// Leaf types must provide a way for code outside to update their internal state.
// This is just a simple replace for now.
impl UpdateLeaf for NumberInput {
type Input = i32;
fn update_mut(&mut self, input: Self::Input) {
self.value = input;
}
}
// dependencies are derived to state what references Dependee nodes need to
// calculate their state on-demand. These could be any number of other Dependees
// or Leafs.
pub struct Components {
left: LeafNode
// A Dependee i.e. its state is a pure transformation of other nodes
pub struct Sum { value: i32, }
// This trait specifies how a Dependee updates its internal state given its dependencies.
impl UpdateDependee for Sum {
fn updatemut(&mut self, input: ComponentsRef is auto-generated by Dependencies. It's a read-reference
// to each field of Components
let ComponentsRef { left, right } = input;
self.value = left.value + right.value;
}
}
struct MyGraph {
left: ArcSumNode is auto-generated by Dependee.
sum: Arc
// Compose a graph! let left = NumberInput::default().intoleaf(); let right = NumberInput::default().intoleaf(); let sum = Sum::default().into_node(Components::new(Arc::clone(&left), Arc::clone(&right)));
let graph = MyGraph { left, right, sum };
// A Visitor is a collection which tracks which nodes have been visited each run.
let mut visitor = HashSet::
// Resolving the graph from any node will traverse via Depth First Search, prompting
// recalculation for an node which has State::Dirty.
//
// Using resolve_root ensures the visitor is cleaned each time, ready for use again.
asserteq!(graph.sum.resolveroot(&mut visitor).value, 0);
// Update the leaves. Any dependent nodes will recompute their internal values. graph.left.update(2); graph.right.update(2);
// We've successfully implemented simple addition! asserteq!(graph.sum.resolveroot(&mut visitor).value, 4); ```
Clearly, to implement a simple addition problem, a dependency graph is
overkill. However, for more complex problems, where many inputs can change
and the output is a combination of many transformations on that input (and
derivations of it), depends can help you produce scalable, performant,
testable code out of the box.
Any graph built using depends can be converted to a Graphviz representation
by passing a GraphvizVisitor (this requires the feature graphviz).
rust
let graph = my_graph();
let mut visitor = GraphvizVisitor::new();
graph.answer.resolve_root(&mut visitor);
assert_eq!(
graph.render().unwrap(),
r#"
digraph G {
2[label="Sum"];
0[label="NumberInput"];
1[label="NumberInput"];
0 -> 2;
1 -> 2;
}
"#);
The graph in the above example is rendered below.
This crate should be considered a Proof Of Concept only and treated with huge amounts of scepticism and distrust.
The guarantees we would like to offer, before considering this crate production-worthy are:
resolve without a change in input, other than when Clean has been implemented incorrectly.Feel free to experiment with the crate, apply it to your problems and pass on any feedback you have.