--- /dev/null
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\DependencyInjection;
+
+use Symfony\Component\DependencyInjection\Exception\BadMethodCallException;
+use Symfony\Component\DependencyInjection\Exception\InvalidArgumentException;
+use Symfony\Component\DependencyInjection\Exception\OutOfBoundsException;
+
+/**
+ * This definition extends another definition.
+ *
+ * @author Johannes M. Schmitt <schmittjoh@gmail.com>
+ */
+class ChildDefinition extends Definition
+{
+ private $parent;
+
+ /**
+ * @param string $parent The id of Definition instance to decorate
+ */
+ public function __construct($parent)
+ {
+ $this->parent = $parent;
+ $this->setPrivate(false);
+ }
+
+ /**
+ * Returns the Definition to inherit from.
+ *
+ * @return string
+ */
+ public function getParent()
+ {
+ return $this->parent;
+ }
+
+ /**
+ * Sets the Definition to inherit from.
+ *
+ * @param string $parent
+ *
+ * @return $this
+ */
+ public function setParent($parent)
+ {
+ $this->parent = $parent;
+
+ return $this;
+ }
+
+ /**
+ * Gets an argument to pass to the service constructor/factory method.
+ *
+ * If replaceArgument() has been used to replace an argument, this method
+ * will return the replacement value.
+ *
+ * @param int|string $index
+ *
+ * @return mixed The argument value
+ *
+ * @throws OutOfBoundsException When the argument does not exist
+ */
+ public function getArgument($index)
+ {
+ if (array_key_exists('index_'.$index, $this->arguments)) {
+ return $this->arguments['index_'.$index];
+ }
+
+ return parent::getArgument($index);
+ }
+
+ /**
+ * You should always use this method when overwriting existing arguments
+ * of the parent definition.
+ *
+ * If you directly call setArguments() keep in mind that you must follow
+ * certain conventions when you want to overwrite the arguments of the
+ * parent definition, otherwise your arguments will only be appended.
+ *
+ * @param int|string $index
+ * @param mixed $value
+ *
+ * @return self the current instance
+ *
+ * @throws InvalidArgumentException when $index isn't an integer
+ */
+ public function replaceArgument($index, $value)
+ {
+ if (is_int($index)) {
+ $this->arguments['index_'.$index] = $value;
+ } elseif (0 === strpos($index, '$')) {
+ $this->arguments[$index] = $value;
+ } else {
+ throw new InvalidArgumentException('The argument must be an existing index or the name of a constructor\'s parameter.');
+ }
+
+ return $this;
+ }
+
+ /**
+ * @internal
+ */
+ public function setAutoconfigured($autoconfigured)
+ {
+ throw new BadMethodCallException('A ChildDefinition cannot be autoconfigured.');
+ }
+
+ /**
+ * @internal
+ */
+ public function setInstanceofConditionals(array $instanceof)
+ {
+ throw new BadMethodCallException('A ChildDefinition cannot have instanceof conditionals set on it.');
+ }
+
+ /**
+ * @internal
+ */
+ public function setBindings(array $bindings)
+ {
+ throw new BadMethodCallException('A ChildDefinition cannot have bindings set on it.');
+ }
+}
+
+class_alias(ChildDefinition::class, DefinitionDecorator::class);