Description

Given an object graph foo.bar.baz, where bar is optional (can be null),
trying to call the property accessor with foo.bar.baz will throw a:

UnexpectedTypeException: PropertyAccessor requires a graph of objects or arrays to operate on, but it found type "NULL" while trying to traverse path "foo.bar.baz" at property "baz".

In some use-cases, it'll be very handy to get null instead of this exception (e.g: in custom validation constraints using a property path set by the developper in annotations).

The flag introduced in #30545 allows to ignore exception on invalid property paths, but it works differently and has some drawbacks:

• paths like foo.bak (non-existing property) will be considered as readable and return null. But foo.bar.baz would still throw the same exception.
• it'll indeed hide potential mistakes in the property path. Which I'd like to avoid for this feature (bar must exist, but can be null).

Then I was about to suggest yet another flag for the PropertyAccessor ($throwOnNullValueInGraph?), but instead, I'm wondering if we shouldn't allow something mimicking the PHP nullsafe_calls RFC 👇

Example

Given an object graph foo.bar.baz, where bar is optional (can be null):

$propertyAccessor = PropertyAccess::createPropertyAccessor();

// Where class Foo has a `bar` property, and class Bar has a `baz` property, for which values are set by the constructors:
$full = new \stdClass();
$full->foo = new Foo(new Bar(new Baz()));

$propertyAccessor->getValue($full, 'foo.bar?.baz') // Would return the Baz instance

$noBar = new \stdClass();
$noBar->foo = new Foo(null);

$propertyAccessor->getValue($noBar, 'foo.bar?.baz') // Would return null

$noBak = new \stdClass();
$noBak->foo = new Foo(new Bar(new Baz()));

$propertyAccessor->getValue($noBak, 'foo.bak?.baz') // Would still throw a NoSuchPropertyException, as property `bak` does not exist in class `Foo`

This wouldn't change anything for writing, only for reading.