Love these videos! I'm tired of content talking about this language as if the viewer hasn't heard about it, there really needs to be more higher concept stuff out there.

This is by far the best understanding of lifetimes I’ve ever heard. So much easier to understand by lifting the hood a little bit

Dude you did hella well with this video. The pace at which you speak, the visuals and the way you explain make this perfectly enjoyable and helpful. Please keep doing this

I thought I understood lifetimes, but this completely reframed my understanding. Well done!

I smashed head-first into the lifetime system about a year ago when I was working on some WASM stuff Tl;Dr I was trying to make a builder pattern struct that carried a reference to a canvas render context for efficiently batching stroke calls I wound up drowning in

Wow, this is so much easier to understand than how rust by example explains it. Awesome video!

This was great. The way lifetimes are usually taught felt like learning some incomplete mental model/abstraction to me. Having to think of "time", aka the temporal aspect of execution, is always hard, whether it's concurrency, event loops, networking, or, as they are taught, lifetimes. Thanks for providing a better mental model that is not as dependent on time.

Thanks. What I found really helpful about this explanation was being shown lifetimes as compound objects. That there are "atomic" lifetimes only correspond to a single variable and that other lifetimes are compounds of these.

please continue the series, it's good to learn new things based what others discovered through great effort

That was the best video about lifetimes I've ever watched! Thank you, leddoo!

I'm currently learning Rust, and to rethink lifetimes as not just time, but memory space makes it so much clearer to what they mean! I like this explanation :)

This is awesome, you have a way of breaking down complex things and using comparison that resonates with me. Looking forward to the borrow checker video.

I think what’s really missing is the for

Good timing. I'm taking freshman-year classes and one of them is discrete computational structures the moment you mentioned lifetimes as subsets of other sets it finally clicked! 😂 two years and I finally fully understood them. Thanks for that!

Great video! I think a very important note about ‘static is that it also refers to owned values when used as a trait bound. That tripped me up when first learning, thinking I effectively required leaked resources if adding that bound

This video explaining Rust's lifetimes is the best I've seen! Looking forward to more from you! Keep it up!

Man that was a good explanation! I skipped lifetimes a bit while learning Rust but this really helped me understand it.

nice explanation! i would recommend closing down your aperture and turning off continuous autofocus and autoexposure during the whiteboard scenes. that way both your face and the drawings can be in focus without any unexpected shifting during the shot

Great video this is probably the clearest explanation of lifetimes I've heard. I think the spatial metaphor is incredibly helpful thank you so much

I still don’t get it…

this is probably the best explanation for lifetimes i've seen. its rewiring my brain.

While less rigorous, I've always read them as "implements" or "at least", as in ... where T "implements" AsRef or ... where 'a (lives for) at least 'b so in the `longest` example: 's1 lives for at least as long as 'out 'out's actual liveness can be determined by the compiler, I'm just making the connection (or even "chain of responsibility") between the out value's lifetime and what it relies on: the inputs.

As a pretty senior developer coming to Rust, this explanation in terms of memory was really helpful to grok the concept. Nice examples, clearly annotated too!

Newbie here, struggling (of course) with Rust concepts. I really like your alternate approach to understanding lifetimes. It helped me a lot.

To me the way to think about lifetime annotations, from a practical perspective, is that they are just a mechanism to tell the compiler the dependency between function arguments and returned value/s; the only case where is no such dependency is when a 'static reference is returned (i.e. the use of global variables as escape hatch). The use of annotations somewhere else is too artificial and unusual IMHO. Also lifetime annotations are only used on references, so, in structs, the annotations are indirectly being applied to inner reference-type fields, possibly under some nested layers.

marvelous, magnificent, stupendous - my brain has expanded thank you

The part about subtyping and outliving of lifetimes is so often overlooked an unexplained. The rewrite you start at 9:35 is, in my opinion, crucial and something that should have been done in The Book. I have done basically the same code (with an attempt at subtyping and variance explanation) in several youtube comments on other "What are lifetime" videos which were lacking.

Re-inventing the wheel trying to fix a problem by making the implementation overly obscure.

Ok. The first three minutes of this video is exceptional!

I will try to use that model in the future let’s see how it goes. Having some more examples would be helpful in those videos I think

Great video! For me as a Rust novice, this interpretation of lifetimes is very intuitive and useful! Looking forward to your next vid!

This one is gold. Give the perception to view the lifetime. Please make more video about lifetime please

Awesome video man! I feel like I couldn't fully wrap my head around lifetimes as explained in the official docs, but after watching the video I now understand the other half of the picture. Thanks for sharing your knowledge!

This was actually very helpful, thank you

Just getting into rust and one thing I wish was clearer was a way to cleanly tell the compiler "this reference will be valid during this scope" i.e. fn foo(bar: impl Iterator) does not compile but for some reason fn foo) does compile and I don't really understand why that lets the compiler accept it I appreciate that this lets it compile but I haven't guaranteed any information about that reference, only named it, but maybe this will enforce that the references in the iterator cannot go out of scope during this function call, if that is the case then I wish that was more obviously written in the lifetimes documentation.

man, what a great video. subscribed! 100k subs with this level of quality content is inevitable.

I'm new to Rust, and ended up developing similar intuition regarding lifetimes. Thanks for validating it - can't wait for the follow up videos. Excellent stuff!

Very insightful! I thought I had a pretty good grasp on lifetimes before watching this video, but it still managed to get looking at them in a completely new way.

8:33 I'm pretty sure 'a is the *intersection* of 'x and 'y, not the union as stated and drawn. That is, the largest lifetime which is fully contained within both 'a and 'b, rather than the smallest lifetime which contains both 'a and 'b

very competent pedagogy, thank you.

sick ass video bro. i was thinking the same thing to with set theory and then you just bring it up. Really gave me a new perspective on it

Thanks for the video. New to Rust as I'm trying to go through a codebase written in Rust. The shear amount of syntax in Rust is overwhelming tbh. This cleared some bits

Thank you! This is the only video that actually makes me understand the concept

Game changing for my understanding of lifetimes. Thanks *so much*!

Subtyping can be unintuitive, but it makes perfect sense for lifetime outlives semantics. Subtype can be naturally used in place of its supertype, much like a reference with outliving lifetime can be substituted in place of another one with lifetime it outlives (assuming covariance). What I found missing about regions is that they still should carry notion of where in code they are alive, and determining what region a reference can point to would still be ultimately determined by liveness and usage. In that sense, this model seems like it would do the same but with an extra step, maybe.

This makes it look like the lifetime is actually a part of the _value_ of the reference rather than the _type,_ which feels _weird._ In example 2, I'd expect it to only be valid if one of the two reassignments was a let-binding, shadowing the previous r with a new r with a different lifetime, meaning a different _type_ according to the model I expected. In most places in Rust, lifetimes are seen as type parameters (either to a struct or a reference) or type constraints, so the lifetime being attached to the value is non-intuitive unless you make references the only values with polymorphic types. Then again, there are higher-rank trait bounds (for

10:54 I understand what you're saying here, but I personally find Rust's trait system a better way of explaining this syntax. 'a: 'b means 'a implements the trait 'b. What does a lifetime mean as a trait? To implement 'a is to be valid for 'a. 'static is therefore only implemented by 'static, and 'static implements every lifetime. Otherwise, great explanation!

Really nice video, man, it helped improving my understanding of lifetimes. Thinking of memory regions made more sense to me.

I never coded anything in rust and I was only aware of lifetime/borrow checker existence but never guessed them to be this deep. Your video is super good nonetheless since I think I got an intuitive understanding of the issue. Thanks! :) In "example_1", I got that the lifetime of r starts when it is being assigned and also an implicit dependency is made to x's "memory region" to be valid (r is only valid if x is valid and usage outside of x being valid causes an error due to attempting to extend r's lifetime outside of x's valid scope) And in "longest" example, I understood that the lifetime of 'out depends on both the lifetime of 's1 and 's2 (both shall have valid "memory region" for 'out to be valid; value of 'out can be anywhere between 's1 and 's2 but not outside of them -> usage of 'out outside of either of 's1 or 's2 valid scope will cause an error due to attempting to extend 'out lifetime where 's1 and/or 's2 no longer have valid "memory region") One thing I don't get is why multiple lifetime parameters in functions (9:33 in video) can't also have their dependency deduced by the compiler instead of requiring explicit outlives constraints? It's more verbose and clearer for me as a reader that s1 and s2 should be allowed to have different lifetimes ('a on both makes me think their lifetimes are linked but it's not since it also has 'a on the output?). I would like to have multiple lifetime parameters but still have the compiler attempting to deduce the lifetime relations itself. Why not both? If I really want to actually tie the lifetime of s1 and s2 then I could use 'a on both but am forced to use something else (e.g. 'out) on return just to be different? And I also lose the compiler's help in deducing the lifetimes relations just because I want to tie s1 and s2's lifetimes? (for whatever reason) Wouldn't it be super simple for the compiler to do this deduction with one less lifetime even?

Incredible explanation. You are genius man 🤯

Fantastic! First time lifetimes have really clicked for me! Thank you!

Very nice alternative view on lifetime understanding, I'll try to apply it in my day to day Rust thinking and see how it helps! Bravo 👏

great video, u have a great way of explaining concepts, keep it up! :)

This video is amazing, great job!

Excellent, clear and concise! Thank you!

wonderful lecture! thanks

Amazing explanation and presentation. Keep 'em comin!

I like to explain lifetimes as ranges on a timeline, where some ranges contain others. This way we can visualize the whole program as a “tree” spanning the duration of the program.

Thank you, this video is a life-saver.

How do you make the animations you have in your videos? I’m working with manim for math stuff, but your coding visuals are very slick

you did a good job on this one! what do you use to create / edit your videos?

great little video, thanks!

I can't help but read fn as 'f*ckin' whenever I look at Rust code

You really helped me out with this one. Thanks.

i don’t know rust so i thought this was some cryptic philosophy take

some folks: "rust has no manual memory management" 'a: 'try, 'me

Amazing stuff! May I know what tool are you using for presentation?

I appreciate the pun in the title.

Best lifetime video ever!

I don't use Rust. I find it great on paper but tedious in practice (although I haven't put much time into it). I still found this video useful and interesting.

Outstanding !! Please more videos centered around this covering various cases that might arise. Also just wondering how would we apply this thinking in this example from the lifetimes chapter in the book: fn longest y.len() { x } else { y } } fn main() { let string1 = String::from("long string is long"); { let string2 = String::from("xyz"); let result = longest(string1.as_str(), string2.as_str()); println!("The longest string is {}", result); } } I mean how we define what region 'a is pointing to?

Great video. It refined my understanding of lifetimes

Very clear! Thank you

'static isn't just leaked allocations/the .data section of the executable a 'static lifetime constraint is also valid for any lifetime always guaranteed to outlive anything in the function/struct

Great video! Thanks!

This is a great video, it really is, and I am sure there are people who don't immediately get a seizure and fall onto the floor when they have to read

still waiting for the struct lifetimes vid!

Lifetimes is actually a generics, but generics for variable scopes instead of types

Very useful, thank you.

I always had this thought when considering the reversed subtype relation with respect to lifetime duration that there was some kind of "duality" here (in maths when you have subset relationship, you get the reversed relation when considering the "duals" of sets instead) You put it very well with the electron analogy, memory region are like the "dual" of time when considering the lifetimes, this was the missing piece I was searching for. Thank you for the enlightment 😁

Brilliant!

Hello, world!

Well done!

Dude i made a video JUST like this i love this perspective of looking at lifetimes

Duddeeeeee! You are awesomeee!

Awesome work, great video! I have an oftopic question. Do you mind sharing the font and color scheme you used for the code example. I find them very easy on the eyes and easy to read, something that I struggle with many other color schemes.

Very nice!

“So let’s think about lifetimes by using the wave-particle duality, a concept that puzzled scientists for decades.” 😅 Thanks for the video

Great video 🙏

lets gooo!!! a new video :D

Still dont understand completely but the regions of memory example is far easier to understand

Great video! Keep it up

Great video 🤘🏽🤘🏽

January can't come soon enough

You always need to think lifetimes in terms of ownership of the pointed-to variable. The data is dropped once the variable goes out of scope. Any lifetime pointing to it must live no longer than the scope of the owned value.

Moreee please

To be honest, the explanation near the end was helpful, but I fail to see how it differs from the "particle" perspective of lifetimes.

8:28, hold on, ch10 of the book says it's the *shorter* of the lifetimes of x and y the example that makes me think this model is wrong goes like this: say you replaced x and y with Strings so that they aren't `static lifetime and if you tried to use l1 after making x go out of scope (and its memory was cleared), it'd still give you an error, even though it points to data owned by y, which would still be valid modeling 'a as a set of memory that l1 can point at, which contains both 'x and 'y, seems to contradict this: that would imply 'a is valid when 'x OR 'y is still valid, but the book says it's while 'x AND 'y are still valid which one is actually correct? I trust the book more than this

here how the 'r can point to &x or &foo while x out of scope? 5:40

10:58 shouldnt it be 'b in 'a because as far as i know 'a: 'b reads as: 'a outlives or lives atleast as long as 'b