Crate calc_graph

Use this crate to split a calculation into related sub-calculations, known as nodes.

You can push information from outside into one or more source nodes, and you can read results from one or more output nodes. Values are only calculated as they're needed, and cached as long as their inputs don't change. This means that recalculations are efficient when you only change some of the inputs, and if you don't request the value from an output node, its value is never calculated.

Example

let graph = Graph::new();                        // create a Graph object
let mut source = graph.source(42);               // define one or more nodes for your inputs
let mut output = source.clone().map(|x| x + 1);  // build one or more nodes for your outputs
assert_eq!(43, output.get_mut());                // read values from your output nodes
 
source.set(99);                                  // push new values to the input nodes...
assert_eq!(100, output.get_mut());               // ...and read the output nodes

Sharing

Func nodes (created by Node::map, Node::zip and related methods) own their inputs (precedent nodes). When you have a node that acts as an input to two or more func nodes, you need to use shared() first. You can then use this shared node multiple times via clone():

let input_node = calc_graph::const_(42).shared();
let mut output1_node = input_node.clone().map(|x| x + 1);
let mut output2_node = input_node.map(|x| x * x);
assert_eq!(43, output1_node.get_mut());
assert_eq!(1764, output2_node.get_mut());

You can have multiple Graph objects in the same program, but when you define a new node, its precedents must come from the same graph.

Boxing

A Node object remembers the full type information of its precedent nodes as well as the closure used to calculate its value. This means that the name of the Node type can be very long, or even impossible to write in the source code. In this situation you can use:

let func_node: Node<Func1<_, i32, _>> = input_node.map(|x| x + 1);
let output_node: BoxNode<i32> = func_node.boxed();

A call to boxed() is also needed if you want a variable that can hold either one or another node; these nodes can have different concrete types, and calling boxed() on each of them gives you a pair of nodes that have the same type.

Threading

Node<Source>, SharedNode and BoxedNode objects are Send and Sync, meaning they can be passed between threads. Calculations are performed on the thread that calls node.get(). Calculations are not parallelised automatically, although you can read separate output nodes from separate threads, even if they share parts of the same graph as inputs.

let graph = Graph::new();
let input_node = graph.source(41);
let output_node = input_node.clone().map(|x| x * x).shared();
assert_eq!(1681, output_node.get());

let t = thread::spawn({
    let input_node = input_node.clone();
    let output_node = output_node.clone();
    move || {
        input_node.update(|n| n + 1);
        output_node.get()
    }
});

assert_eq!(1764, t.join().unwrap());

input_node.update(|n| n + 1);
assert_eq!(1849, output_node.get());

Structs

Const	Calculates a node's value by returning the same value every time.
Func1	Calculates a value from another node.
Func2	Calculates a value from 2 nodes.
Func3	Calculates a value from 3 nodes.
Func4	Calculates a value from 4 nodes.
Func5	Calculates a value from 5 nodes.
Func6	Calculates a value from 6 nodes.
Func7	Calculates a value from 7 nodes.
Func8	Calculates a value from 8 nodes.
Graph	Returns new Node<Source> objects, which act as inputs to the rest of the graph.
Lazy	Calculates a node's value by calling a function on demand and caching the result.
Node	Represents a value within the graph.
Source	Holds a value that can be updated directly from outside the graph.

Traits

Calc	Calculates a node's value.

Functions

const_	Returns a node whose value never changes.
lazy	Returns a node whose value is calculated once on demand and cached.

Type Definitions

BoxNode	A node returned by Node::boxed.
SharedNode	A node returned by Node::shared.