Add immutable Failure/Success futures

lib/Failure.php

@@ -0,0 +1,59 @@
+<?php
+
+namespace Alert;
+
+/**
+ * A placeholder for a resolved failure
+ */
+class Failure implements Future {
+    private $error;
+
+    public function __construct(\Exception $error) {
+        $this->error = $error;
+    }
+
+    /**
+     * Pass the Future to the specified callback upon completion regardless of success or failure
+     *
+     * @param callable $onComplete
+     */
+    public function onComplete(callable $onComplete) {
+        call_user_func($onComplete, $this);
+    }
+
+    /**
+     * Has the Future completed (succeeded/failure is irrelevant)?
+     *
+     * @return bool
+     */
+    public function isComplete() {
+        return TRUE;
+    }
+
+    /**
+     * Has the Future value been successfully resolved?
+     *
+     * @return bool
+     */
+    public function succeeded() {
+        return FALSE;
+    }
+
+    /**
+     * Retrieve the value that successfully fulfilled the Future
+     *
+     * @throws \Exception
+     */
+    public function getValue() {
+        throw $this->error;
+    }
+
+    /**
+     * Retrieve the Exception responsible for Future resolution failure
+     *
+     * @return \Exception
+     */
+    public function getError() {
+        return $this->error;
+    }
+}

lib/Success.php

@@ -0,0 +1,59 @@
+<?php
+
+namespace Alert;
+
+/**
+ * A placeholder for a successfully resolved value
+ */
+class Success implements Future {
+    private $value;
+
+    public function __construct($value = NULL) {
+        $this->value = $value;
+    }
+
+    /**
+     * Pass the Future to the specified callback upon completion regardless of success or failure
+     *
+     * @param callable $onComplete
+     */
+    public function onComplete(callable $onComplete) {
+        call_user_func($onComplete, $this);
+    }
+
+    /**
+     * Has the Future completed (success is irrelevant)?
+     *
+     * @return bool
+     */
+    public function isComplete() {
+        return TRUE;
+    }
+
+    /**
+     * Has the Future value been successfully resolved?
+     *
+     * @return bool
+     */
+    public function succeeded() {
+        return TRUE;
+    }
+
+    /**
+     * Retrieve the value that successfully fulfilled the Future
+     *
+     * @return mixed
+     */
+    public function getValue() {
+        return $this->value;
+    }
+
+    /**
+     * Retrieve the Exception responsible for Future resolution failure
+     *
+     * @return NULL
+     */
+    public function getError() {
+        return NULL;
+    }
+}