PHP 7.4: How to check if typed property is initialized (including initialization with null)?

Question

I have class A:

class A
{
    private ?string $typed;

    public function isTypedInitialized(): bool
    {
        // ???
    }
}

How to check if $this->typed was already initialized with any value including null? isset() doesn't meet my needs, because it returns false for null.

PHP doesn't care about initialization. But why use nullable if you want it initialized to a meaningful value. What does initialization mean to you in this case? — Sherif
– Sherif, Commented Sep 13, 2021 at 18:27
it is for caching. If it is initialized, the data is cached and we return it from property. The data may be null as well. — Audiophile
– Audiophile, Commented Sep 13, 2021 at 18:40

Valentin Gerbey · Accepted Answer · 2021-09-13 18:37:28Z

5

I've done this check while deserialising a request to an object and checking for initialisation was a part of validation process. The solution was to use a reflection, in your example the code would be like this:

public function isTypedInitialized(): bool
{
    return (new ReflectionClass(self::class))
        ->getProperty('typed')
        ->isInitialized($this);
}

But I don't think that this checking should be the part of same class

answered Sep 13, 2021 at 18:37

Valentin Gerbey

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1 Comment

Audiophile Over a year ago

I'd expect something like is_initialized(), but... We have what we have.

Jacques Marcotte · Accepted Answer · 2022-08-15 04:49:19Z

If you don't want to instantiate an entire Reflection object or deal with having to use the string representation of the property (which is harder for some IDEs to understand and can be more prone to human error) you can also just rely on PHP throwing an Error if you attempt to read an uninitialized property.

public function isTypedInitialized(): bool
{
    try {
        $this->typed; // attempt to read, PHP will throw if uninitialized
        return true;
    } catch (\Error $e) {
        return false;
    }
}

If you're not yet on PHP 8.1, this is also a decent way of mimicking readonly properties:

public function setTyped(string $typed): self
{
    try {
        $this->typed; // attempt to read
    } catch (\Error $e) {
        $this->typed = $typed; // typed is uninitialized, so is ok to set
        return $this;
    }

    // if it gets here, that means PHP read the typed property without issue,
    // which means that it was already initialized.
    throw new \LogicException('property `typed` is already set');
}

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