Added Specification pattern

Specification/AbstractSpecification.php

@@ -0,0 +1,53 @@
+<?php
+namespace DesignPatterns\Specification;
+
+/**
+ * An abstract specification allows the creation of wrapped specifications
+ */
+abstract class AbstractSpecification implements SpecificationInterface
+{
+    /**
+     * Checks if given item meets all criteria
+     * 
+     * @param Item $item
+     * 
+     * @return bool
+     */
+    public function isSatisfiedBy(Item $item)
+    {
+    }
+
+    /**
+     * Creates a new logical AND specification
+     * 
+     * @param SpecificationInterface $spec
+     * 
+     * @return SpecificationInterface
+     */
+    public function plus(SpecificationInterface $spec)
+    {
+        return new Plus($this, $spec);
+    }
+
+    /**
+     * Creates a new logical OR composite specification
+     * 
+     * @param SpecificationInterface $spec
+     * 
+     * @return SpecificationInterface
+     */
+    public function either(SpecificationInterface $spec)
+    {
+        return new Either($this, $spec);
+    }
+
+    /**
+     * Creates a new logical NOT specification
+     * 
+     * @return SpecificationInterface
+     */
+    public function not()
+    {
+        return new Not($this);
+    }
+}