PHP Internals News: Episode 100: Sealed Classes

Thursday, March 24th 2022, 09:04 GMT

In this episode of "PHP Internals News" I talk with Saif Eddin Gmati (Website, Twitter, GitHub) about the "Sealed Classes" RFC that he has proposed.

The RSS feed for this podcast is https://derickrethans.nl/feed-phpinternalsnews.xml, you can download this episode's MP3 file, and it's available on Spotify and iTunes. There is a dedicated website: https://phpinternals.news

Transcript

Derick Rethans 0:14: Hi, I'm Derick. Welcome to PHP internals news, the podcast dedicated to explaining the latest developments in the PHP language. This is episode 100. Today I'm talking with Saif Eddin Gmati about the sealed classes RFC that they're proposing. Saif, would you please introduce yourself?
Saif Eddin Gmati 0:31: Hello, my name is Saif Eddin Gmati. I work as a Senior programmer at Les-Tilleuls.coop. I'm an open source enthusiast and contributor.
Derick Rethans 0:39: Let's dive straight into this RFC. What is the problem that you're trying to solve with it?
Saif Eddin Gmati 0:43: Sealed classes just like enums and tagged unions allow developers to define their data models in a way where invalid state becomes less likely. It also eliminates the need to handle unknown subtypes for a specific model, as using sealed classes to define models gives us an idea on what child types would be available at run time. Sealing also provides us with a way for restricting inheritance or the use of a specific trait. For example, if we look at logger trait from the PSR log package that could be sealed to logger interface. This way, we ensure that every use of this trait is coming from a logger not from any other class.
Derick Rethans 1:24: I'm just reading through this RFC tomorrow, again, and something I didn't pick up on reading to it last time. It states that PHP already has sort of two sealed classes.
Unknown Speaker 1:35: Yes, the throwable class in PHP can only be implemented by extending either error or exception. The same applies for DateTime interface, which can only be implemented by extending DateTime class or DateTime Immutable class.
Derick Rethans 1:52: Because PHP itself doesn't allow you to implement either throwable or DateTimeInterface. I haven't quite realized that that these are also sealed classes really. What is sort of the motivation behind wanting to introduce sealed classes?
Unknown Speaker 2:06