On my own, I've basically learned the 101, and 201 sections of this talk. Even some of the 301 section I knew, like how Trait Objects are represented, she doesn't go into the vtables. I always saw Trait Objects as runtime polymorphism, with traits as compile time polymorphism, both forms through composition rather than inheritance. What didn't dawn on me, was the possibility to operate over heterogeneous collections by boxing Trait Objects. That is really cool, and a perfectly example of when to use heap allocation. I like how in Rust you can make these high-level trade-offs that are impossible in most languages.
I agree! I knew it was *possible* to do stuff like the heterogeneous collections w/ vectors of boxed types, but it hadn’t really dawned on me as a common use case.
Just for the record, Box is not the only way to get Trait Objects and heterogeneous collections. Any kind of (fat) pointer / reference suffices: Box but also &Trait, as well as Rc etc. And nowadays it is preferred to prefix a Trait name with the 'dyn' keyword to better disambiguate between the trait itself (which is NOT a type) and the dynamic trait object type: Box, &dyn Trait
I think she is a great speaker as well. The only thing that I missed was how the call was implemented behind the scenes. How does the program know which method to call on which "abstract" Cast?
Basically, a trait object consists of two pointers (effectively, a "fat pointer"). One part points to the struct memory, the other part points to the impl of the trait for that struct.
This was indeed a great lecture and she is a great teacher. I wrote everything down while watching the video (easier to follow and understand, especially in 301). In case someone wants to try the "source code", it can be found here: github.com/lightern/rust/blob/master/DD.rs
dyn wasn't in Rust when the presentation was made, it was introduced later to create trait objects. in earlier versions using a trait in the place of a type would implicitly mean a trait object (impl Trait didn't exist then either)
Thank you for this video. It cleared up for me a number of questions I had about Traits -- which are a little like Java's interfaces, but far more powerful. I won't even mention Java! :D
I think I'm missing the point here. What I took away from this talk is that I can replace a primitive or a Vec with a Trait for no reason. I feel like I understood traits better before I watched this, but everyone else is saying this talk was great. I realize she chose simple examples on purpose, but these are cases where traits shouldn't be used.
I don't get it. How does a typical OO background make traits hard to understand? Also, for a "deep dive", this doesn't dive very deep. I was hoping to learn the differences between using generics on a trait and having a type field.
Great talk! I'll have to say that as for trait objects I've read the two chapters in the book on traits multiple times and I'm not sure the name is appropriate. It's misleading a think because a trait object (unless I'm totally off base) seems nothing like an object in other languages. The implementations themselves are what bring behavior. It's not packaged with the data like in a traditional object. If you "create" a trait object by saying Vec then you aren't creating an object at all. It's more similar to trait bounds the way I see it. You are restricting what the smart pointer (box) points at by defining that it must be something that implements the cast trait. I think the name should be changed maybe, because I think the name 'trait object' is very misleading. If anyone can draw a parallel to traditional objects in other languages to justify the name I'd love to see one. I don't actually think the parallel she drew made sense because we don't package up the pointer with a method in the same location. Am I totally off base here?!
`Box` is a *fat pointer* that contains both a pointer to the data and a pointer to the vtable (virtual table) that has pointers to the method implementations.
I know rust's OO has its unique. But from what described here, I don't see difference compare to C++ or Java. Anybody can make it more explicit, what's the difference.
There really isn't one. Traits are basically just interfaces. The difference is mostly historical. Rust uses them by default, consistently, everywhere (especially the standard library) and for every thing, since it started. Unlike in C++ or Java, they weren't added as an optional patch to the (retrospectively obvious) disaster that is the traditional inheritance model. The general theme in Rust is that it doesn't really contain anything new. It just has the hindsight of what worked and didn't work in C, C++, Haskel and others and has benefit of fresh start. A lot of stuff that became "standard/recommended practice" in these is the default way in Rust, often enforced by compiler itself.
The naming convention for the trait names is horrible. It would be much more intuitive to use names like in swift protocols. Instead of a Hash trait it would be Hashable. Instead of Cast it would be Castable. It makes type and trait names different. A Hash is something that is a hash of something and Hashable is something that can be hashed.
She is decisive and speaks extremely clearly and with good force. I like it !!!
Great teacher. The DnD metaphor should be incorporated into the official Rust book.
But using the full rulebook, not simplified.
and also a playable demo. ;-)
DnD are specific to Western understanding, never learnt about dnd in Asia.
@@7xr1e20ln8 as long as you've played an rpg though...
DnD 3r(ust)
Tremendous talk. I hope we hear more from Nell in the future. Great communicator.
That was awesome! I'd love to see a tutorial series on Rust for newcomers in this kind of format.
totally agree
This is a terrific presentation. Really helped me understand some concepts I had questions about.
I can not thank Nell enough for this incredibly well done explainer! The DND metaphor really helped.
I wish more Rust talks were like this! The visuals really sold it for me.
I came across this video today and I think this is the best explanation of Traits in Rust on the internet!
Great introduction, with clear and powerful delivery. Thank you!
This is so dense I'm gonna have to watch it like 5 times.. incredible work by the speaker.
On my own, I've basically learned the 101, and 201 sections of this talk. Even some of the 301 section I knew, like how Trait Objects are represented, she doesn't go into the vtables. I always saw Trait Objects as runtime polymorphism, with traits as compile time polymorphism, both forms through composition rather than inheritance. What didn't dawn on me, was the possibility to operate over heterogeneous collections by boxing Trait Objects. That is really cool, and a perfectly example of when to use heap allocation. I like how in Rust you can make these high-level trade-offs that are impossible in most languages.
I agree! I knew it was *possible* to do stuff like the heterogeneous collections w/ vectors of boxed types, but it hadn’t really dawned on me as a common use case.
If you are coming from C++, in C++20 there will be a std::polymorphic_value which will act as Box
Just for the record, Box is not the only way to get Trait Objects and heterogeneous collections. Any kind of (fat) pointer / reference suffices:
Box but also &Trait, as well as Rc etc.
And nowadays it is preferred to prefix a Trait name with the 'dyn' keyword to better disambiguate between the trait itself (which is NOT a type) and the dynamic trait object type: Box, &dyn Trait
Amazing talk. Very clear, entertaining and easy to follow!
Great job! This helped getting me started on wrapping my head around traits.
The video game example is really good for understanding traits.
Just starting Rust, and I was confused about traits, and this pretty much cleared it up, Thanks
This helps me a lot for understanding trait and trait bound which I've been confusing about for a week .👍👍👍
I love this video makes it so clear
She is amazing, she can teach how to code in PHP and will not be boring.
what if the half orc learns to speak elvish on her travels?
Thanks a lot for such an impressive talk!!
Doesn't trait objects require `dyn` keyword? Was that added later on?
very clear explanation. Thank you for sharing this video.
We could really use more of this type of thing!
This is an amazing talk for newcomers
Great video, traits were actually quite difficult to wrap my head around at first
This was a great talk. Helped me learn about the Trait objects
I think she is a great speaker as well. The only thing that I missed was how the call was implemented behind the scenes. How does the program know which method to call on which "abstract" Cast?
Basically, a trait object consists of two pointers (effectively, a "fat pointer"). One part points to the struct memory, the other part points to the impl of the trait for that struct.
This was indeed a great lecture and she is a great teacher. I wrote everything down while watching the video (easier to follow and understand, especially in 301). In case someone wants to try the "source code", it can be found here: github.com/lightern/rust/blob/master/DD.rs
Great presentation.
Excellent presentation! Thank you!!
Great talk!!
good job on not laughing each time she said "castrate"
Fantastic speaker.
18:41 should be Vec
dyn wasn't in Rust when the presentation was made, it was introduced later to create trait objects. in earlier versions using a trait in the place of a type would implicitly mean a trait object (impl Trait didn't exist then either)
Thank you for this video. It cleared up for me a number of questions I had about Traits -- which are a little like Java's interfaces, but far more powerful. I won't even mention Java! :D
Next: how to fight and vanquish the borrow checker with half orc barbarian and elf wizard
I think I'm missing the point here. What I took away from this talk is that I can replace a primitive or a Vec with a Trait for no reason. I feel like I understood traits better before I watched this, but everyone else is saying this talk was great. I realize she chose simple examples on purpose, but these are cases where traits shouldn't be used.
Excellent presentation. great job
wonderful explanation.
great talk, thank you nell
Very informative and inspirational
One part that is missing is how to link a character to a spell-book. it is the character that throws the spells not the spellbook.
Excellent talk thank you so much!
isn't it Box
Super nice explanation!
You got me at cast trait!
I don't get it. How does a typical OO background make traits hard to understand?
Also, for a "deep dive", this doesn't dive very deep. I was hoping to learn the differences between using generics on a trait and having a type field.
Great talk! I'll have to say that as for trait objects I've read the two chapters in the book on traits multiple times and I'm not sure the name is appropriate. It's misleading a think because a trait object (unless I'm totally off base) seems nothing like an object in other languages. The implementations themselves are what bring behavior. It's not packaged with the data like in a traditional object. If you "create" a trait object by saying Vec then you aren't creating an object at all. It's more similar to trait bounds the way I see it. You are restricting what the smart pointer (box) points at by defining that it must be something that implements the cast trait. I think the name should be changed maybe, because I think the name 'trait object' is very misleading. If anyone can draw a parallel to traditional objects in other languages to justify the name I'd love to see one. I don't actually think the parallel she drew made sense because we don't package up the pointer with a method in the same location. Am I totally off base here?!
Traits are, IMO, like interface assignments in Go. You can pass around trait objects like in Go you can pass around interface objects.
`Box` is a *fat pointer* that contains both a pointer to the data and a pointer to the vtable (virtual table) that has pointers to the method implementations.
awesome intro to traits
❤
I know rust's OO has its unique. But from what described here, I don't see difference compare to C++ or Java.
Anybody can make it more explicit, what's the difference.
There really isn't one. Traits are basically just interfaces. The difference is mostly historical. Rust uses them by default, consistently, everywhere (especially the standard library) and for every thing, since it started. Unlike in C++ or Java, they weren't added as an optional patch to the (retrospectively obvious) disaster that is the traditional inheritance model.
The general theme in Rust is that it doesn't really contain anything new. It just has the hindsight of what worked and didn't work in C, C++, Haskel and others and has benefit of fresh start. A lot of stuff that became "standard/recommended practice" in these is the default way in Rust, often enforced by compiler itself.
brb... gotta learn D&D first :(
ok never mind.. This is amazing...
I'm recently waiting for some dnd or coc game in real life, and, I found one here.....
Who else had their volume turned up when they clicked this?
Yeah, watching a quiet video beforehand on headphones, clearly reminds you that how important sound-volume normalization SHOULD HAVE BEEN in youtube.
The naming convention for the trait names is horrible. It would be much more intuitive to use names like in swift protocols. Instead of a Hash trait it would be Hashable. Instead of Cast it would be Castable. It makes type and trait names different. A Hash is something that is a hash of something and Hashable is something that can be hashed.
thank you, ur comment helped me.a.lot. it s obvious now, but.it obvious.now.that.u.mentionned it
she looks like Michael Reeves
This is exactly why we need more women in tech, they make things easy to understand.
What the hell does the quality of an explanation have to do with the gender? :D
Some people just have gift to teach and some don't. Gender have nothing to do with it.
vacuous statement. She has high energy and is passionate, that's about that
Too slow and not enough real information.
So slow. For little kids?