initial commit

Author: floriankugler

.gitignore

@@ -0,0 +1,8 @@
+.DS_Store
+/.build
+/Packages
+xcuserdata/
+DerivedData/
+.swiftpm/configuration/registries.json
+.swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
+.netrc

LICENSE.md

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2023 objc.io
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

Package.swift

@@ -0,0 +1,24 @@
+// swift-tools-version: 6.0
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "AttributeGraph",
+    products: [
+        // Products define the executables and libraries a package produces, making them visible to other packages.
+        .library(
+            name: "AttributeGraph",
+            targets: ["AttributeGraph"]),
+    ],
+    targets: [
+        // Targets are the basic building blocks of a package, defining a module or a test suite.
+        // Targets can depend on other targets in this package and products from dependencies.
+        .target(
+            name: "AttributeGraph"),
+        .testTarget(
+            name: "AttributeGraphTests",
+            dependencies: ["AttributeGraph"]
+        ),
+    ]
+)

README.md

@@ -0,0 +1,4 @@
+# Swift Talk
+## Attribute Graph (Part 2)
+
+This is the code that accompanies Swift Talk Episode 430: [Attribute Graph (Part 2)](https://talk.objc.io/episodes/S01E430-attribute-graph-part-2)

Sources/AttributeGraph/AttributeGraph.swift

@@ -0,0 +1,111 @@
+// Based on https://www.semanticscholar.org/paper/A-System-for-Efficient-and-Flexible-One-Way-in-C%2B%2B-Hudson/9609985dbef43633f4deb88c949a9776e0cd766b
+// https://repository.gatech.edu/server/api/core/bitstreams/3117139f-5de2-4f1f-9662-8723bae97a6d/content
+
+final class AttributeGraph {
+    var nodes: [AnyNode] = []
+    var currentNode: AnyNode?
+
+    func input<A>(name: String, _ value: A) -> Node<A> {
+        let n = Node(name: name, in: self, wrappedValue: value)
+        nodes.append(n)
+        return n
+    }
+
+    func rule<A>(name: String, _ rule: @escaping () -> A) -> Node<A> {
+        let n = Node(name: name, in: self, rule: rule)
+        nodes.append(n)
+        return n
+    }
+
+    func graphViz() -> String {
+        let nodesStr = nodes.map {
+            "\($0.name)\($0.potentiallyDirty ? " [style=dashed]" : "")"
+        }.joined(separator: "\n")
+        let edges = nodes.flatMap(\.outgoingEdges).map {
+            "\($0.from.name) -> \($0.to.name)\($0.pending ? " [style=dashed]" : "")"
+        }.joined(separator: "\n")
+        return """
+        digraph {
+        \(nodesStr)
+        \(edges)
+        }
+        """
+    }
+}
+
+protocol AnyNode: AnyObject {
+    var name: String { get }
+    var outgoingEdges: [Edge] { get }
+    var incomingEdges: [Edge] { get set }
+    var potentiallyDirty: Bool { get set }
+}
+
+final class Edge {
+    unowned var from: AnyNode
+    unowned var to: AnyNode
+    var pending = false
+
+    init(from: AnyNode, to: AnyNode) {
+        self.from = from
+        self.to = to
+    }
+}
+
+final class Node<A>: AnyNode {
+    unowned var graph: AttributeGraph
+    var name: String
+    var rule: (() -> A)?
+    var incomingEdges: [Edge] = []
+    var outgoingEdges: [Edge] = []
+    var potentiallyDirty: Bool = false {
+        didSet {
+            guard potentiallyDirty, potentiallyDirty != oldValue else { return }
+            for e in outgoingEdges {
+                e.to.potentiallyDirty = true
+            }
+        }
+    }
+
+    private var _cachedValue: A?
+
+    var wrappedValue: A {
+        get {
+            recomputeIfNeeded()
+            return _cachedValue!
+        }
+        set {
+            assert(rule == nil)
+            _cachedValue = newValue
+            for e in outgoingEdges {
+                e.pending = true
+                e.to.potentiallyDirty = true
+            }
+        }
+    }
+
+    func recomputeIfNeeded() {
+        if let c = graph.currentNode {
+            let edge = Edge(from: self, to: c)
+            outgoingEdges.append(edge)
+            c.incomingEdges.append(edge)
+        }
+        if _cachedValue == nil, let rule {
+            let previousNode = graph.currentNode
+            defer { graph.currentNode = previousNode }
+            graph.currentNode = self
+            _cachedValue = rule()
+        }
+    }
+
+    init(name: String, in graph: AttributeGraph, wrappedValue: A) {
+        self.name = name
+        self.graph = graph
+        self._cachedValue = wrappedValue
+    }
+
+    init(name: String, in graph: AttributeGraph, rule: @escaping () -> A) {
+        self.name = name
+        self.graph = graph
+        self.rule = rule
+    }
+}

Tests/AttributeGraphTests/AttributeGraphTests.swift

@@ -0,0 +1,40 @@
+import Testing
+@testable import AttributeGraph
+
+@Test func example() async throws {
+    let graph = AttributeGraph()
+    let a = graph.input(name: "A", 10)
+    let b = graph.input(name: "B", 20)
+    let c = graph.rule(name: "C") { a.wrappedValue + b.wrappedValue }
+    let d = graph.rule(name: "D") { c.wrappedValue * 2 }
+    #expect(d.wrappedValue == 60)
+
+    let str = """
+    digraph {
+    A
+    B
+    C
+    D
+    A -> C
+    B -> C
+    C -> D
+    }
+    """
+    #expect(str == graph.graphViz())
+
+    a.wrappedValue = 40
+    #expect(d.wrappedValue == 120)
+
+    let str2 = """
+    digraph {
+    A
+    B
+    C [style=dashed]
+    D [style=dashed]
+    A -> C [style=dashed]
+    B -> C
+    C -> D
+    }
+    """
+    #expect(str2 == graph.graphViz())
+}