Update documentation and code style.

Author: drupol

README.md

@@ -29,7 +29,8 @@ It provides different trees implementations:
 
 Exporters and importers:
 * **Ascii**: Export a tree into an ascii graphic, just for swag and visualisation fun.
-* **Graph**: Export a tree into a graph using the [graphp/graphp](https://github.com/graphp/graph) library.
+* **Graph**: Export a tree into a Graph using the [graphp/graphp](https://github.com/graphp/graph) library.
+* **GraphViz**: Export a tree into a script in [GraphViz](http://www.graphviz.org/) format.
 * **Text**: Export a tree into a simple string, easy for storing in a database.
 
 Modifier:
@@ -51,8 +52,7 @@ Blog post: [https://not-a-number.io/2018/phptree-a-fast-tree-implementation](htt
 
 ## Optional packages
 
-* [graphp/graphp](https://github.com/graphp/graph): To convert a tree into a graph.
-* [graphp/graphviz](https://github.com/graphp/graphviz): To render a graph into dot format or an image.
+* [graphp/graphp](https://github.com/graphp/graph): To export a tree into a Graph.
 
 ## Usage
 
@@ -61,8 +61,7 @@ Blog post: [https://not-a-number.io/2018/phptree-a-fast-tree-implementation](htt
 
 declare(strict_types = 1);
 
-use Graphp\GraphViz\GraphViz;
-use drupol\phptree\Exporter\Graph;
+use drupol\phptree\Exporter\Gv;
 use drupol\phptree\Node\ValueNode;
 use drupol\phptree\Exporter\Text;
 
@@ -79,14 +78,15 @@ foreach (\range('A', 'Z') as $v) {
 // Add children to the root node.
 $tree->add(...$nodes);
 
-// Export to an image.
-$graphViz = new GraphViz();
-$graphExporter = new Graph();
-$graphViz->display($graphExporter->export($tree));
-
 // Export to text.
 $textExporter = new Text();
 echo $textExporter->export($tree); // [root[A[C[G[O][P]][H[Q][R]]][D[I[S][T]][J[U][V]]]][B[E[K[W][X]][L[Y][Z]]][F[M][N]]]]⏎
+
+// Export to a GraphViz script.
+$exporter = new Gv();
+$dotScript = $exporter->export($tree);
+file_put_contents('graph.gv', $dotScript);
+// Then do "dot -Tsvg graph.gv -o graph.svg" to export the script to SVG.
 ```
 
 ## Code quality, tests and benchmarks

src/Exporter/Gv.php

@@ -16,11 +16,12 @@ class Gv implements ExporterInterface
     /**
      * The graph attributes.
      *
-     * @var string[]
+     * @var string[]|string[][]
      */
     private $attributes = [];
+
     /**
-     * Is the graph directed or undirected.
+     * The graph type.
      *
      * @var bool
      */
@@ -31,10 +32,6 @@ class Gv implements ExporterInterface
      */
     public function export(NodeInterface $node): string
     {
-        $directed = true === $this->getDirected() ?
-            '->' :
-            '--';
-
         $attributes = '';
         foreach ($this->attributes as $key => $attribute) {
             if (\is_string($attribute)) {
@@ -72,7 +69,7 @@ public function export(NodeInterface $node): string
             $edges .= \sprintf(
                 '  "%s" %s "%s";' . "\n",
                 $this->getHash($parent),
-                $directed,
+                true === $this->getDirected() ? '->' : '--',
                 $this->getHash($child)
             );
         }
@@ -92,7 +89,7 @@ public function getDirected(): bool
     }
 
     /**
-     * Set the graph as directed.
+     * Set the graph type, directed or undirected.
      *
      * @param bool $directed
      *   True for a directed graph, false otherwise.

src/Node/AttributeNodeInterface.php

@@ -13,6 +13,7 @@ interface AttributeNodeInterface extends NaryNodeInterface
      * {@inheritdoc}
      */
     public function getAttribute($key);
+
     /**
      * {@inheritdoc}
      */

src/Node/Node.php

@@ -37,6 +37,7 @@ public function __clone()
     {
         $this->storage = clone $this->storage;
 
+        /** @var \drupol\phptree\Node\NodeInterface $child */
         foreach ($this->children() as $child) {
             $child->setParent($this);
         }
@@ -63,15 +64,14 @@ public function all(): \Traversable
     {
         yield $this;
 
-        foreach ($this->children() as $candidate) {
-            yield from $candidate->all();
+        /** @var \drupol\phptree\Node\NodeInterface $child */
+        foreach ($this->children() as $child) {
+            yield from $child->all();
         }
     }
 
     /**
      * {@inheritdoc}
-     *
-     * @return \drupol\phptree\Node\NodeInterface|\Traversable
      */
     public function children(): \Traversable
     {
@@ -137,6 +137,7 @@ public function depth(): int
      */
     public function find(NodeInterface $node): ?NodeInterface
     {
+        /** @var \drupol\phptree\Node\NodeInterface $candidate */
         foreach ($this->all() as $candidate) {
             if ($candidate === $node) {
                 return $node;
@@ -201,6 +202,7 @@ public function height(): int
     {
         $height = $this->depth();
 
+        /** @var \drupol\phptree\Node\NodeInterface $child */
         foreach ($this->children() as $child) {
             $height = \max($height, $child->height());
         }

src/Node/NodeInterface.php

@@ -23,15 +23,15 @@ public function add(NodeInterface ...$node): NodeInterface;
     /**
      * Get all the nodes of a tree including the parent node itself.
      *
-     * @return \drupol\phptree\Node\NodeInterface|\Traversable
+     * @return \Traversable
      *   The node.
      */
     public function all(): \Traversable;
 
     /**
      * Get the children.
      *
-     * @return \drupol\phptree\Node\NodeInterface|\Traversable
+     * @return \Traversable
      *   The children
      */
     public function children(): \Traversable;

src/Storage/StorageInterface.php

@@ -15,7 +15,7 @@ interface StorageInterface
      * @param string $key
      *   The identifier name of the value.
      *
-     * @return null|int|mixed|string
+     * @return mixed
      *   The value.
      */
     public function get($key);