|
The <code>receiver1</code> forwards the request to <code>receiver2</code>, which in turn forwards the request to <code>receiver3</code>, which handles (performs) the request.
== ExamplesExample ==
<!-- Wikipedia is not a list of examples. Do not add examples from your favorite programming language here; this page exists to explain the design pattern, not to show how it interacts with subtleties of every language under the sun. Feel free to add examples here: http://en.wikibooks.org/wiki/Computer_Science_Design_Patterns/Chain_of_responsibility -->
=== C++ example ===
This C++11 implementation is based on the pre C++98 implementation in the book.<ref>{{cite book |author=Erich Gamma |title=Design Patterns: Elements of Reusable Object-Oriented Software |publisher=Addison Wesley |year=1994 |isbn=0-201-63361-2 |pages=189 ff.}}</ref>
<syntaxhighlight lang="c++">
{{wikibooks|Computer Science Design Patterns|Chain of responsibility|Chain-of-responsibility implementations in various languages}}
=== PHP example ===
<syntaxhighlight lang="php">
<?php
abstract class Logger
{
/**
* Bitmask flags for severity.
*/
public const NONE = 0;
public const INFO = 0b000001;
public const DEBUG = 0b000010;
public const WARNING = 0b000100;
public const ERROR = 0b001000;
public const FUNCTIONAL_MESSAGE = 0b010000;
public const FUNCTIONAL_ERROR = 0b100000;
public const ALL = 0b111111;
/** @var int A bitmask flag from this class. */
protected int $logMask;
/** @var \Logger|null An optional next logger to handle the message */
protected ?Logger $next = null;
/**
* Logger constructor.
*
* @param int $mask
* A bitmask flag from this class.
*/
public function __construct(int $mask)
{
$this->logMask = $mask;
}
/**
* Set next responsible logger in the chain.
*
* @param \Logger $nextLogger
* Next responsible logger.
*
* @return \Logger
* Logger: Next responsible logger.
*/
public function setNext(Logger $nextLogger): Logger
{
$this->next = $nextLogger;
return $nextLogger;
}
/**
* Message writer handler.
*
* @param string $msg
* Message string.
* @param int $severity
* Severity of message as a bitmask flag from this class.
*
* @return $this
*/
public function message(string $msg, int $severity): Logger
{
if ($severity & $this->logMask) {
$this->writeMessage($msg);
}
if ($this->next !== null) {
$this->next->message($msg, $severity);
}
return $this;
}
/**
* Abstract method to write a message
*
* @param string $msg
* Message string.
*/
abstract protected function writeMessage(string $msg): void;
}
class ConsoleLogger extends Logger
{
protected function writeMessage(string $msg): void
{
echo "Writing to console: $msg\n";
}
}
class EmailLogger extends Logger
{
protected function writeMessage(string $msg): void
{
echo "Sending via email: $msg\n";
}
}
class FileLogger extends Logger
{
protected function writeMessage(string $msg): void
{
echo "Writing to a log file: $msg\n";
}
}
$logger = new ConsoleLogger(Logger::ALL);
$logger
->setNext(new EmailLogger(Logger::FUNCTIONAL_MESSAGE | Logger::FUNCTIONAL_ERROR))
->setNext(new FileLogger(Logger::WARNING | Logger::ERROR));
$logger
// Handled by ConsoleLogger since the console has a loglevel of all
->message("Entering function ProcessOrder().", Logger::DEBUG)
->message("Order record retrieved.", Logger::INFO)
// Handled by ConsoleLogger and FileLogger since filelogger implements Warning & Error
->message("Customer Address details missing in Branch DataBase.", Logger::WARNING)
->message("Customer Address details missing in Organization DataBase.", Logger::ERROR)
// Handled by ConsoleLogger and EmailLogger as it implements functional error
->message("Unable to Process Order ORD1 Dated D1 For Customer C1.", Logger::FUNCTIONAL_ERROR)
// Handled by ConsoleLogger and EmailLogger
->message("Order Dispatched.", Logger::FUNCTIONAL_MESSAGE);
/* Output
Writing to console: Entering function ProcessOrder().
Writing to console: Order record retrieved.
Writing to console: Customer Address details missing in Branch DataBase.
Writing to a log file: Customer Address details missing in Branch DataBase.
Writing to console: Customer Address details missing in Organization DataBase.
Writing to a log file: Customer Address details missing in Organization DataBase.
Writing to console: Unable to Process Order ORD1 Dated D1 For Customer C1.
Sending via email: Unable to Process Order ORD1 Dated D1 For Customer C1.
Writing to console: Order Dispatched.
Sending via email: Order Dispatched.
*/
</syntaxhighlight>
== Implementations ==
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