Add option to apply default values from the schema

Author: erayd

README.md

@@ -79,6 +79,37 @@ is_bool($request->processRefund); // true
 is_int($request->refundAmount); // true
 ```
 
+### Default Values
+
+If your schema contains default values, you can have these automatically applied during validation:
+
+```php
+<?php
+
+use JsonSchema\Validator;
+use JsonSchema\Constraints\Factory;
+use JsonSchema\Constraints\Constraint;
+
+$request = (object)[
+    'refundAmount'=>17
+];
+
+$validator = new Validator(new Factory(null, null, Constraint::CHECK_MODE_APPLY_DEFAULTS));
+
+$validator->check($request, (object)[
+    "type"=>"object",
+    "properties"=>(object)[
+        "processRefund"=>(object)[
+            "type"=>"boolean",
+            "default"=>true
+        ]
+    ]
+]); //validates, and sets defaults for missing properties
+
+is_bool($request->processRefund); // true
+$request->processRefund; // true
+```
+
 ### With inline references
 
 ```php

src/JsonSchema/Constraints/Constraint.php

@@ -27,6 +27,7 @@ abstract class Constraint implements ConstraintInterface
 
     const CHECK_MODE_NORMAL = 		0x00000001;
     const CHECK_MODE_TYPE_CAST = 	0x00000002;
+    const CHECK_MODE_APPLY_DEFAULTS =   0x00000004;
 
     /**
      * @var Factory

src/JsonSchema/Constraints/ObjectConstraint.php

@@ -143,6 +143,12 @@ public function validateDefinition(&$element, $objectDefinition = null, JsonPoin
             $definition = $this->getProperty($objectDefinition, $i);
 
             if (is_object($definition)) {
+                // Set default values
+                if ($this->factory->getCheckMode() & self::CHECK_MODE_APPLY_DEFAULTS && isset($definition->default) && $property === $undefinedConstraint) {
+                    $this->setProperty($element, $i, $definition->default);
+                    $property = &$this->getProperty($element, $i, $undefinedConstraint);
+                }
+
                 // Undefined constraint will check for is_object() and quit if is not - so why pass it?
                 $this->checkUndefined($property, $definition, $path, $i, $coerce);
             }
@@ -169,6 +175,22 @@ protected function &getProperty(&$element, $property, $fallback = null)
         return $fallback;
     }
 
+    /**
+     * set and return a property on an object or array
+     *
+     * @param mixed $element Element to manipulate
+     * @param string $property  Property to set
+     * @param mixed $value Value to set
+     */
+    protected function setProperty(&$element, $property, $value)
+    {
+        if (is_array($element)) {
+            $element[$property] = $value;
+        } elseif (is_object($element)) {
+            $element->$property = $value;
+        }
+    }
+
     /**
      * validating minimum and maximum property constraints (if present) against an element
      *