PHP Internals News: Episode 100: Sealed Classes PHP Internals News
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PHP Internals News: Episode 100: Sealed Classes
London, UK
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
The main motivation for this feature comes from Hack the programming language. Hack contains a lot of interesting type concepts that I think personally, PHP could benefit from and sealed classes is one of those concepts.
Derick Rethans 2:18
What kind of syntax are you proposing?
Saif Eddin Gmati 2:21
The syntax I'm proposing actually there is three syntax options for the RFC currently, but the main syntax is inspired by both Hack and Java. It's more similar to the syntax used in Java as Hack uses attributes. Personally, I have been I guess, using attributes from the start as I personally see sealing and finalizing similar as both effects how inheritance work for a specific class. Having sealed implemented as an attribute while final uses a keyword brings more inconsistency into the language which is why I have decided not to include attributes as a syntax option.
Derick Rethans 2:56
In my opinion, attributes shouldn't be used for any kind of syntax things. What they shoul
PHP Internals News: Episode 100: Sealed Classes
London, UK
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
The main motivation for this feature comes from Hack the programming language. Hack contains a lot of interesting type concepts that I think personally, PHP could benefit from and sealed classes is one of those concepts.
Derick Rethans 2:18
What kind of syntax are you proposing?
Saif Eddin Gmati 2:21
The syntax I'm proposing actually there is three syntax options for the RFC currently, but the main syntax is inspired by both Hack and Java. It's more similar to the syntax used in Java as Hack uses attributes. Personally, I have been I guess, using attributes from the start as I personally see sealing and finalizing similar as both effects how inheritance work for a specific class. Having sealed implemented as an attribute while final uses a keyword brings more inconsistency into the language which is why I have decided not to include attributes as a syntax option.
Derick Rethans 2:56
In my opinion, attributes shouldn't be used for any kind of syntax things. What they shoul