Use of traits vs extending abstract classes

[erikaraujo]

Hi,

I was reading the tempest documentation (huge fan of the framework already!) and noticed a pattern of using traits instead of simply extending abstract classes.

Examples:

final class Book implements DatabaseModel
{
    use IsDatabaseModel;
    
    //...
}

final readonly class RedisCache implements Cache
{
    use IsCache;

    //...
}

final class BookRequest implements Request
{
    use IsRequest;

    //...
}

I'm sure there's a reason behind this decision - I was just wondering, however, what the reason is.

Thanks!

[brendt]

Good question!

• I made a video about it here: https://www.youtube.com/watch?v=HK9W5A-Doxc
• I wrote a blog post about it here: https://stitcher.io/blog/extends-vs-implements
• And it's originally inspired by this blog post: https://lwn.net/Articles/548560/

The tl;dr is: using traits + interfaces is more flexible than classic inheritance, and it's inspired by more modern languages like Go and Rust.

[erikaraujo]

I haven't yet watched the video, but I did just read your blog post. I think (still processing, though 😅) I disagree.

Taking your own example from the article:

An example: User extends Model, for me, that's wrong: a User isn't a Model; instead it's a class that can act like a model.

And your trait methods: IsDatabaseModel. Doesn't that say the User is a DatabaseModel in the end?
But maybe I didn't quite understand that sentence I quoted.

I do appreciate the consistency, though - in my opinion it is what matters the most.

And, just to be clear, I don't mean to try and convince you to change anything. Just hoping for a healthy debate/conversation here.

[erikaraujo]

Literally right after I wrote the whole thing, I think I got it. So the User can be a DatabaseModel, but using traits, it can also be something else - like a DTO, for example?
And, in this case, you'd just go like User implements DatabaseModel, Dto and use IsDto?

Yea, I'm pretty sure I got it.

(maybe that's a terrible example, but ¯\(ツ)/¯ )

[brendt]

That's a pretty good example! You got it :) another one: a user CAN authenticate, it CAN havr an avatar, ... but it IS not one of those things