DAG aware artifact builder

Rust crate for managing the building of artifacts by builders which are connected in a directed acyclic graph (DAG) like manner.

This crate provides essentially a cache which keeps artifacts of builders in order to prevent the same builder to produce multiple equal artifacts. This could be useful if the builders use consumable resources to create their artifacts, the building is a heavyweight procedure, or a given DAG dependency structure among the builders shall be properly preserved among their artifacts.

The basic principal on which this crate is build, suggests two levels of abstraction, the builder level and the artifact level. Each builder type has one specific artifact type. The builders are represented by any struct, which implements the Builder trait, which in turn has an associate type that specifies the artifact type.

Builders are supposed to be wrapped in ArtifactPromises, which prevents to call its build() method directly. However, the ArtifactPromise acts like an Rc and thus allows to share one instance among several dependants. This Rc-like structure creates naturally a DAG.

For building a Builder, its build() method is provided with a ArtifactResolver that allows to resolve depending ArtifactPromises into their respective artifacts, which is, in order to form a DAG, wrapped behind a Rc.

As entry point serves the ArtifactCache, which allows to resolve any ArtifactPromise to its artifact outside of a Builder. The ArtifactCache is essentially a cache. It can be used to translate any number of ArtifactPromises, sharing their common dependencies. Consequently, resolving the same ArtifactPromise using the same ArtifactCache results in the same Rced artifact.

When artifacts shall be explicitly recreated, e.g. to form a second independent artifact DAG, ArtifactCache has a clear() method to reset the cache. Additionally, ArtifactCache has an invalidate() method to remove a single builder artifact including its dependants (i.e. those artifacts which had used the invalidated one).

Example

```rust use std::rc::Rc; use daab::*;

// Simple artifact struct Leaf { //... }

// Simple builder struct BuilderLeaf { // ... } impl BuilderLeaf { pub fn new() -> Self { Self { // ... } } } impl Builder for BuilderLeaf { type Artifact = Leaf;

fn build(&self, _cache: &mut ArtifactResolver) -> Self::Artifact {
    Leaf{
        // ...
    }
}

}

// Composed artifact, linking to a Leaf struct Node { leaf: Rc, // Dependency artifact // ... }

// Composed builder, depending on BuilderLeaf struct BuilderNode { builderleaf: ArtifactPromise, // Dependency builder // ... } impl BuilderNode { pub fn new(builderleaf: ArtifactPromise) -> Self { Self { builder_leaf, // ... } } } impl Builder for BuilderNode { type Artifact = Node;

fn build(&self, cache: &mut ArtifactResolver) -> Self::Artifact {
    // Resolve ArtifactPromise to its artifact
    let leaf = cache.resolve(&self.builder_leaf);

    Node {
        leaf,
        // ...
    }
}

}

fn main() { // The cache to storing already created artifacts let mut cache = ArtifactCache::new();

// Constructing builders
let leaf_builder = ArtifactPromise::new(BuilderLeaf::new());

let node_builder_1 = ArtifactPromise::new(BuilderSimpleNode::new(leaf_builder.clone()));
let node_builder_2 = ArtifactPromise::new(BuilderSimpleNode::new(leaf_builder.clone()));

// Using the cache to access the artifacts from the builders

// The same builder results in same artifact
assert!(Rc::ptr_eq(&cache.get(&node_builder_1), &cache.get(&node_builder_1)));

// Different builders result in different artifacts
assert!( ! Rc::ptr_eq(&cache.get(&node_builder_1), &cache.get(&node_builder_2)));

// Different artifacts may link the same dependent artifact
assert!(Rc::ptr_eq(&cache.get(&node_builder_1).leaf, &cache.get(&node_builder_2).leaf));

} ```