Hi Lydia,
I understand where you are coming from because I encountered this a few
times myself, but every time it was actually because I was doing something
wrong. The reason for this limitation is actually very simple and logical.
Let me explain.
When you use untyped properties, the type is not restricted so every
property can be nullable by default. It's very simple for the language to
have NULL as the default value for all untyped properties.
When using typed properties, the language cannot use NULL as the default
anymore because the type might not allow NULL, e.g public string $name
allows only string values. Unless you assign some string value to it, the
language will not initialize it with any value. If you need the property to
have a state indicating no value, you can make it nullable and assign NULL
as the default value.
What you are proposing is actually not acceptable from the type system's
point of view. We cannot add a new syntax for assigning default values to
type properties. It might make sense in a very limited scope, e.g. public !
int $number; defaults to 0, but in any other more complex scenario, this
fails miserably. Consider this example:
class Test {
public ! MyObject&SomeInterface $prop1;
public ! int|false|null $prop2;
}
In the example above, what default values could be assigned to the
properties? The correct answer is none. You cannot have a default object,
nor can you pick a default value from the union of three types. There is
simply no way to determine the default value. So if we had a new syntax
like this, it would be severely limited to only the simplest scenarios.
This would create a new inconsistency for the benefit of using a single
character instead of assigning the value. There would be no benefit to
introducing such inconsistency to the language.
It is the job of the developer to specify the default type. Some things can
be left for PHP to infer, but when it comes to the default property value,
the developer needs to assign it.
You said that an isset is necessary when using typed properties. I would
argue that an isset is not needed. Using isset with typed properties is a
code smell in many circumstances. If the property can be unassigned, the
developer should use a sentinel value such as null to indicate this. If the
property is always expected to hold a value, then the code should not allow
a path to access it before it's initialized.
Kind Regards,
Kamil
