Add some notes

typestatetest.php

@@ -0,0 +1,95 @@
+<?php
+
+// Examples: Query builder, file, socket.
+
+interface ClosedFile
+{
+    public function open();
+}
+
+interface OpenFile
+{
+    public function read();
+    public function close();
+}
+
+interface CannotOpen {}
+
+class MyFile implements ClosedFile, OpenFile, CannotOpen
+{
+    /**
+     * @self-out ClosedFile
+     */
+    public function __construct() {
+    }
+    /**
+     * @self-out OpenFile|CannotOpen
+     */
+    public function open() {
+        // if can't open, throw exception and invalidate $this
+    }
+    /**
+     * @self-out ClosedFile
+     */
+    public function close() {
+    }
+    /**
+     * @return string
+     */
+    public function read() {
+        return 'content';
+    }
+}
+
+$file = new MyFile("somefile");
+$file->open();
+if ($file instanceof OpenFile) {
+    $content = $file->read();
+    $file->close();
+} elseif ($file instanceof CannotOpen) {
+    // Mooo.
+}
+
+for ($i = 1; $i < 10; ++$i) {
+    // TODO: What here?
+    $file->open();
+}
+
+// ClosedFile
+$file = new MyFile("somefile");
+if ($file instanceof OpenFile) {
+    // TODO: Impossible
+}
+if (hardcomputation()) {
+    $file->open();
+}
+// $file is OpenFile|ClosedFile|CannotOpen
+// TODO: Have to check state?
+
+/**
+ * @param OpenFile $file
+ */
+function readall(OpenFile $file) {
+    $file->read();
+    $file->close(); // TODO: Not allowed to change state of aliased variable.
+    return $file; // TODO: Not allowed to transfer ownership
+}
+
+/**
+ * @param string $name
+ * @return ClosedFile
+ */
+function makefile($name) {
+    // ClosedFile
+    $file = new File($name);
+    dosomething($file);  // Can't change state, still closed
+    return $file;  // Owner can change
+}
+
+/**
+ * @param ClosedFile $file
+ * @param-out OpenFile $file
+ */
+function open(ClosedFile &$file)
+{
+}