SIC - Simple [Dependency] Injection Container

gistfile1.php

<?php
namespace sic;

/**
 * Simple [Dependency] Injection Container
 *
 * @author  Michal Wachowski <wachowski.michal@gmail.com>
 * @license New BSD License
 */
class SIC {

	protected $definitions = array();
	protected $instances = array();

	/**
	 * Constructor
	 *
	 * @param array $definitions array containing definitions
	 */
	public function __construct($definitions = array()) {
		if($definitions === array()) {
			return;
		}

		foreach($definitions as $name => $definition) {
			$this->set($name, $definition);
		}
	}

	/**
	 * Returns defined object instance or value from container
	 * If instance is shared - returns it by reference
	 *
	 * @param string $name name of retrieved definition
	 *
	 * @return mixed
	 * @throws \InvalidArgumentException
	 */
	public function & get($name) {
		if(!$this->exists($name)) {
			throw new \InvalidArgumentException(sprintf('Definition for %s not found', $name));
		}

		$result = null;
		if($this->shared($name) && $this->instances[$name] !== null) {
			return $this->instances[$name];
		}

		$result = is_callable($this->definitions[$name]) ? $this->definitions[$name]($this) : $this->definitions[$name];
		if($this->shared($name)) {
			$this->instances[$name] = $result;
		}

		return $result;
	}

	/**
	 * Adds definition to container
	 * If definition under name exists - will be overwritten
	 *
	 * @param string   $name       name for further retrieval
	 * @param callable $definition definition, callable or value
	 * @param bool     $shared     if true - first retrieval is stored, and all following will return stored value
	 *
	 * @return $this
	 */
	public function set($name, $definition, $shared = false) {
		$this->drop($name);

		if(is_callable($definition) && $shared === true) {
			$this->instances[$name] = null;
		}

		$this->definitions[$name] = $definition;

		return $this;
	}

	/**
	 * Remove definition from container
	 *
	 * @param string $name dropped definition name
	 *
	 * @return $this
	 */
	public function drop($name) {
		if($this->exists($name)) {
			unset($this->definitions[$name]);
		}

		if($this->shared($name)) {
			unset($this->instances[$name]);
		}

		return $this;
	}

	/**
	 * Returns true if definition exists
	 *
	 * @param string $name checked definition name
	 *
	 * @return bool
	 */
	public function exists($name) {
		return array_key_exists($name, $this->definitions);
	}

	/**
	 * Returns true if definition is shared
	 *
	 * @param string $name
	 *
	 * @return bool
	 */
	public function shared($name) {
		return array_key_exists($name, $this->instances);
	}

}