PHP design pattern code examples of null object (25)

objective

The empty object pattern is not a GOF design pattern, but it is enough to be considered a design pattern as a frequent pattern. It has the following advantages:

The client code is simple
It can reduce the probability of null pointer exception
Test cases don’t need to consider too many conditions

Return an object or null should be replaced by a return object or nullobject. Nullobject simplifies rigid code and eliminates condition checking in client code, such as if (! Is)_ Null ($obj)) {$obj – > callsomething();} just $obj – > callsomething().

example

Symfony2: empty log
Symfony2: empty output of symfony / console
Empty command in command line mode
Empty processor in chain of responsibility mode

UML diagram

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code

Service.php

logger = $logger;
    }

    /**
     *What to do...
     *'we are in service: dosomething' is returned in the diary.
     */
    public function doSomething()
    {
        //Tip: Here you just use it, not through_ Null () checks if $logger is set.
        $this->logger->log('We are in '.__METHOD__);
    }
}

LoggerInterface.php

PrintLogger.php

NullLogger.php

test

Tests/LoggerTest.php

expectOutputString('');
        $service->doSomething();
    }

    /**
     *Test the printlogger object. If you contact the above, you can know that designpatterns / behavioral / nullobject / service:: dosomething has been written in the journal.
     */
    public function testStandardLogger()
    {
        $service = new Service(new PrintLogger());
        $this->expectOutputString('We are in DesignPatterns\Behavioral\NullObject\Service::doSomething');
        $service->doSomething();
    }
}

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