'What does question mark do in php? [duplicate]

class Service
{
    private Logger $logger;

    public function __construct(
        ?Logger $logger = null,
    ) {
        $this->logger = $logger ?? new NullLogger();
    }
}

I'm learning php oop.

What does question mark do in ?Logger $logger = null??

I googled but couldn't find an answer.

phpphp-8.1


Solution 1:[1]

"?" in front of argument or property means that this argument/property is nullabe, in your example you can pass either a Logger object or null.

You can read more about it here: https://www.php.net/manual/en/migration71.new-features.php

Solution 2:[2]

This is Nullable type.

PHP Documentation

Sources

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Source: Stack Overflow

Solution Source
Solution 1 ikyuchukov
Solution 2

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