PHP Internals News: Episode 99: Allow Null and False as Standalone Types

PHP Internals News: Episode 99: Allow Null and False as Standalone Types

Thursday, March 10th 2022, 09:04 GMT London, UK

In this episode of "PHP Internals News" I talk with George Peter Banyard (Website, Twitter, GitHub, GitLab) about the "Allow Null and False as Standalone Types" RFC that he has proposed.

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Transcript

Derick Rethans 0:15

Hi, I'm Derick. Welcome to PHP internals news, a podcast dedicated to explain the latest developments in the PHP language. This is episode 99. Today I'm talking with George Peter Banyard, about the Allow null and false at standalone types RFC that he's proposing. Hello, George Peter, would you please introduce yourself?

George Peter Banyard 0:36

Hello, my name is George Peter Banyard. I work on the PHP language, and I'm an Imperial student in maths in my free time.

Derick Rethans 0:44

Are you're trying to say you're a student in your free time or contribute to PHP in your free time?

George Peter Banyard 0:49

I feel like at this time, it's like, both are true at the same time.

Derick Rethans 0:53

Let's hop into this RFC. It is titled allow null and false as standalone types. What is the problem that it is trying to solve?

George Peter Banyard 1:02

This is the second iteration of this RFC. So the first one was to just allow null initially, and null is the unit type In type theory parlance of PHP, ie the type which only has one value. So null is a type and a value. And the main issue is that when for leads more with like inhabitants, and like the Liskov substitution principle. If you have like a method, like the parent method, which can be told like either null or an object, and your implementation in a child class always returns null, for various reasons, maybe because it doesn't support this feature, or whatever is out, or... If your child method only returns null, currently, you can't document, that you can't type this properly, you can document it in a doc comment or something like that. But due to how PHP type handling works, you need to specify at least like another type with null in the union. Basically resort to always saying like mimicking the parent signature, when you could be more specific. This was the main use case I initially went into.

Derick Rethans 2:08

If I understand correctly, you can't just have an inherited method that has hinted as to just return null?

George Peter Banyard 2:14

Exactly. If you always return null, maybe because you always work or something like that, then you must still declare the return type as like null or exception, which is not a concrete because you say what, like why never fail. And like static analysers, if they can figure it out that you're using a child class, they can't maybe li