Every ending marks a new beginning, and today, is the beginning of a new chapter for me. Ten years ago I took a leap into the unknown, today I take another. After a decade of working on Sentry I move on to start something new. Sentry has been more than just a job, it has been a defining part of my life. A place where I've poured my energy, my ideas, my heart. It has shaped me, just as I've shaped it. And now, as I step away, I do so with immense gratitude, a deep sense of pride, and a heart full of memories. From A Chance Encounter I've known David, Sentry's co-founder (alongside Chris), long before I was ever officially part of the team as our paths first crossed on IRC in the Django community. Even my first commit to Sentry predates me officially working there by a few years. Back in 2013, over conversations in the middle of Russia — at a conference that, incidentally, also led to me meeting my wife — we toyed with the idea of starting a company together. That exact plan didn't materialize, but the seeds of collaboration had been planted. Conversations continued, and by late 2014, the opportunity to help transform Sentry (which already showed product market fit) into a much bigger company was simply too good to pass up. I never could have imagined just how much that decision would shape the next decade of my life. To A Decade of Experiences For me, Sentry's growth has been nothing short of extraordinary. At first, I thought reaching 30 employees would be our ceiling. Then we surpassed that, and the milestones just kept coming — reaching a unicorn valuation was something I once thought was impossible. While we may have stumbled at times, we've also learned immensely throughout this time. I'm grateful for all the things I got to experience and there never was a dull moment. From representing Sentry at conferences, opening an engineering office in Vienna, growing teams, helping employees, assisting our licensing efforts and leading our internal platform teams. Every step and achievement drove me. Yet for me, the excitement and satisfaction of being so close to the founding of a company, yet not quite a founder, has only intensified my desire to see the rest of it. A Hard Goodbye Walking away from something you love is never easy and leaving Sentry is hard. Really hard. Sentry has been woven into the very fabric of my adult life. Working on it hasn't just spanned any random decade; it perfectly overlapped with marrying my wonderful wife, and growing our family from zero to three kids. And will it go away entirely? The office is right around the corner afterall. From now on, every morning, when I will grab my coffee, I will walk past it. The idea of no longer being part of the daily decisions, the debates, the momentum — it feels surreal. That sense of belonging to a passionate team, wrestling with tough decisions, chasing big wins, fighting fires together, sometimes venting about our missteps and discussing absurd and ridiculous trivia became part of my identity. There are so many bright individuals at Sentry, and I'm incredibly proud of what we have built together. Not just from an engineering point of view, but also product, marketing and upholding our core values. We developed SDKs that support a wide array of platforms from Python to JavaScript to Swift to C++, lately expanding to game consoles. We stayed true to our Open Source principles, even when other options were available. For example, when we needed an Open Source PDB implementation for analyzing Windows crashes but couldn't find a suitable solution, we contributed to a promising Rust crate instead of relying on Windows VMs and Microsoft's dbghelp. When we started, our ingestion system handled a few thousand requests per second — now it handles well over a million. While building an SDK may seem straightforward, maintaining and updating them to remain best-in-class over the years requires immense dedication. It takes determination to build something that works out of the box with little configuration. A lot of clever engineering and a lot of deliberate tradeoffs went into the product to arrive where it is. And ten years later, is a multi-product company. What started with just crashes, now you can send traces, profiles, sessions, replays and more. We also stuck to our values. I'm pleased that we ran experiments with licensing despite all the push back we got over the years. We might not have found the right solution yet, but we pushed the conversation. The same goes for our commitment to funding of dependencies. And Heartfelt Thank You I feel an enormous amount of gratitude for those last ten years. There are so many people I owe thanks to. I owe eternal thanks to David Cramer and Chris Jennings for the opportunity and trust they placed in me. To Ben Vinegar for his unwavering guidance and support. To Dan Levine, for investing in us and believing in our vision. To Daniel Griesser, for being an exceptional first hire in Vienna, and shepherding our office there and growing it to 50 people. To Vlad Cretu, for bringing structure to our chaos over the years. To Milin Desai for taking the helm and growing us. And most of all, to my wonderful wife, Maria — who has stood beside me through every challenge, who has supported me when the road was uncertain, and who has always encouraged me to forge my own path. To everyone at Sentry, past and present — thank you. For the trust, the lessons, the late nights, the victories. For making Sentry what it is today. Quo eo? I'm fully aware it's a gamble to believe my next venture will find the same success as Sentry. The reality is that startups that achieve the kind of scale and impact Sentry has are incredibly rare. There's a measure of hubris in assuming lightning strikes twice, and as humbling as that realization is, it also makes me that much more determined. The creative spark that fueled me at Sentry isn't dimming. Not at all in fact: it burns brighter fueld by the feeling that I can explore new things, beckoning me. There's more for me to explore, and I'm ready to channel all that energy into a new venture. Today, I stand in an open field, my backpack filled with experiences and a renewed sense of purpose. That's because the world has changed a lot in the past decade, and so have I. What drives me now is different from what drove me before, and I want my work to reflect that evolution. At my core, I'm still inspired by the same passion — seeing others find value in what I create, but my perspective has expanded. While I still take great joy in building things that help developers, I want to broaden my reach. I may not stray far from familiar territory, but I want to build something that speaks to more people, something that, hopefully, even my children will find meaningful. Watch this space, as they say.

Three years ago I shared the As-Any Hack on this blog. That hack is a way to get upcasting to supertraits working on stable Rust. To refresh your memory, the goal was to make something like this work: #[derive(Debug)] struct AnyBox(Box<dyn DebugAny>); trait DebugAny: Any + Debug {} impl<T: Any + Debug + 'static> DebugAny for T {} The problem? Even though DebugAny inherits from Any, Rust wouldn't let you use methods from Any on a dyn DebugAny. So while you could call DebugAny methods just fine, trying to use downcast_ref from Any (the reason to use Any in the first place) would fail: fn main() { let any_box = AnyBox(Box::new(42i32)); dbg!(any_box.0.downcast_ref::<i32>()); // Compile error } The same would happen if we tried to cast it into an &dyn Any? A compile error again: fn main() { let any_box = AnyBox(Box::new(42i32)); let any = &*any_box.0 as &dyn Any; dbg!(any.downcast_ref::<i32>()); } But there is good news! As of Rust 1.86, this is finally fixed. The cast now works: At the time of writing, this fix is in the beta channel, but stable release is just around the corner. That means a lot of old hacks can finally be retired. At least once your MSRV moves up. Thank you so much to everyone who worked on this to make it work! For completeness' sake here is the extension map from the original block post cleaned up so that it does not need the as-any hack: use std::any::{Any, TypeId}; use std::cell::{Ref, RefCell, RefMut}; use std::collections::HashMap; use std::fmt::Debug; trait DebugAny: Any + Debug {} impl<T: Any + Debug + 'static> DebugAny for T {} #[derive(Default, Debug)] pub struct Extensions { map: RefCell<HashMap<TypeId, Box<dyn DebugAny>>>, } impl Extensions { pub fn insert<T: Debug + 'static>(&self, value: T) { self.map .borrow_mut() .insert(TypeId::of::<T>(), Box::new(value)); } pub fn get<T: Default + Debug + 'static>(&self) -> Ref<'_, T> { self.ensure::<T>(); Ref::map(self.map.borrow(), |m| { m.get(&TypeId::of::<T>()) .and_then(|b| (&**b as &dyn Any).downcast_ref()) .unwrap() }) } pub fn get_mut<T: Default + Debug + 'static>(&self) -> RefMut<'_, T> { self.ensure::<T>(); RefMut::map(self.map.borrow_mut(), |m| { m.get_mut(&TypeId::of::<T>()) .and_then(|b| ((&mut **b) as &mut dyn Any).downcast_mut()) .unwrap() }) } fn ensure<T: Default + Debug + 'static>(&self) { if self.map.borrow().get(&TypeId::of::<T>()).is_none() { self.insert(T::default()); } } }

Sometimes in Rust, you need to convert a string into a value of a specific type (for example, converting a string to an integer). For this, the standard library provides the rather useful FromStr trait. In short, FromStr can convert from a &str into a value of any compatible type. If the conversion fails, an error value is returned. It's unfortunately not guaranteed that this value is an actual Error type, but overall, the trait is pretty useful. It has however a drawback: it takes a &str and not a String which makes it wasteful in situations where your input is a String. This means that you will end up with a useless clone if do not actually need the conversion. Why would you do that? Well consider this type of API: let arg1: i64 = parser.next_value()?; let arg2: String = parser.next_value()?; In such cases, having a conversion that works directly with String values would be helpful. To solve this, we can introduce a new trait: FromString, which does the following: Converts from String to the target type. If converting from String to String, bypass the regular logic and make it a no-op. Implement this trait for all uses of FromStr that return a error that can be converted into Box<dyn Error> upon failure. We start by defining a type alias for our error: pub type Error = Box<dyn std::error::Error + Send + Sync + 'static>; You can be more creative here if you want. The benefit of using this directly is that a lot of types can be converted into that error, even if they are not errors themselves. For instance a FromStr that returns a bare String as error can leverage the standard library's blanket conversion implementation to Error. Then we define the FromString trait: pub trait FromString: Sized { fn from_string(s: String) -> Result<Self, Error>; } To implement it, we provide a blanket implementation for all types that implement FromStr, where the error can be converted into our boxed error. As mentioned before, this even works for FromStr where Err: String. We also add a special case for when the input and output types are both String, using transmute_copy to avoid a clone: use std::any::TypeId; use std::mem::{ManuallyDrop, transmute_copy}; use std::str::FromStr; impl<T> FromString for T where T: FromStr<Err: Into<Error>> + 'static, { fn from_string(s: String) -> Result<Self, Error> { if TypeId::of::<T>() == TypeId::of::<String>() { Ok(unsafe { transmute_copy(&ManuallyDrop::new(s)) }) } else { T::from_str(&s).map_err(Into::into) } } } Why transmute_copy? We use it instead of the regular transmute? because Rust requires both types to have a known size at compile time for transmute to work. Due to limitations a generic T has an unknown size which would cause a hypothetical transmute call to fail with a compile time error. There is nightly-only transmute_unchecked which does not have that issue, but sadly we cannot use it. Another, even nicer solution, would be to have specialization, but sadly that is not stable either. It would avoid the use of unsafe though. We can also add a helper function to make calling this trait easier: pub fn from_string<T, S>(s: S) -> Result<T, Error> where T: FromString, S: Into<String>, { FromString::from_string(s.into()) } The Into might be a bit ridiculous here (isn't the whole point not to clone?), but it makes it easy to test this with static string literals. Finally here is an example of how to use this: let s: String = from_string("Hello World").unwrap(); let i: i64 = from_string("42").unwrap(); Hopefully, this utility is useful in your own codebase when wanting to abstract over string conversions. If you need it exactly as implemented, I also published it as a simple crate. Postscriptum: A big thank-you goes to David Tolnay and a few others who pointed out that this can be done with transmute_copy. Another note: TypeId::of call requires V to be 'static. This is okay for this use, but there are some hypothetical cases where this is not helpful. In that case there is the excellent typeid crate which provides a ConstTypeId, which is like TypeId but is constructible in const in stable Rust.

The concept of purity — historically a guiding principle in social and moral contexts — is also found in passionate, technical discussions. By that I mean that purity in technology translates into adherence to a set of strict principles, whether it be functional programming, test-driven development, serverless architectures, or, in the case of Rust, memory safety. Memory Safety Rust positions itself as a champion of memory safety, treating it as a non-negotiable foundation of good software engineering. I love Rust: it's probably my favorite language. It probably won't surprise you that I have no problem with it upholding memory safety as a defining feature. Rust aims to achieve the goal of memory safety via safe abstractions, a compile time borrow checker and a type system that is in service of those safe abstractions. It comes as no surprise that the Rust community is also pretty active in codifying a new way to reason about pointers. In many ways, Rust pioneered completely new technical approaches and it it widely heralded as an amazing innovation. However, as with many movements rooted in purity, what starts as a technical pursuit can evolve into something more ideological. Similar to how moral purity in political and cultural discourse can become charged, so does the discourse around Rust, which has been dominated by the pursuit of memory safety. Particularly within the core Rust community itself, discussion has moved beyond technical merits into something akin to ideological warfare. The fundamental question of “Is this code memory safe?”, has shifted to “Was it made memory safe in the correct way?”. This distinction matters because it introduces a purity test that values methodology over outcomes. Safe C code, for example, is often dismissed as impossible, not necessarily because it is impossible, but because it lacks the strict guarantees that Rust's borrow checker enforces. Similarly, using Rust’s unsafe blocks is increasingly frowned upon, despite their intended purpose of enabling low-level optimizations when necessary. This ideological rigidity creates significant friction when Rust interfaces with other ecosystems (or gets introduced there), particularly those that do not share its uncompromising stance. For instance, the role of Rust in the Linux kernel has been a hot topic. The Linux kernel operates under an entirely different set of priorities. While memory safety is important there is insufficient support for adopting Rust in general. The kernel is an old project and it aims to remain maintainable for a long time into the future. For it to even consider a rather young programming language should be seen as tremendous success for Rust and also for how open Linus is to the idea. Yet that introduction is balanced against performance, maintainability, and decades of accumulated engineering expertise. Many of the kernel developers, who have found their own strategies to write safe C for decades, are not accepting the strongly implied premise that their work is inherently flawed simply because it does not adhere to Rust's strict purity rules. Tensions rose when a kernel developer advocating for Rust's inclusion took to social media to push for changes in the Linux kernel development process. The public shaming tactic failed, leading the developer to conclude: It's not just the kernel where Rust's memory safety runs up against the complexities of the real world. Very similar feelings creep up in the gaming industry where people love to do wild stuff with pointers. You do not need large disagreements to see the purist approach create some friction. A recent post of mine for instance triggered some discussions about the trade-offs between more dependencies, and moving unsafe to centralized crates. I really appreciate that Rust code does not crash as much. That part of Rust, among many others, makes it very enjoyable to work with. Yet I am entirely unconvinced that memory safety should trump everything, at least at this point in time. What people want in the Rust in Linux situation is for the project leader to come in to declare support for Rust's call for memory safety above all. To make the detractors go away. Python's Migration Lesson Hearing this call and discussion brings back memories. I have lived through a purity driven shift in a community before. The move from Python 2 to Python 3 started out very much the same way. There was an almost religious movement in the community to move to Python 3 in a ratcheting motion. The idea that you could maintain code bases that support both 2 and 3 were initially very loudly rejected. I took a lot of flak at the time (and for years after) for advocating for a more pragmatic migration which burned me out a lot. That feedback came both in person and online and it largely pushed me away from Python for a while. Not getting behind the Python 3 train was seen as sabotaging the entire project. However, a decade later, I feel somewhat vindicated that it was worth being pragmatic about that migration. At the root of that discourse was a idealistic view of how Unicode could work in the language and that you can move an entire ecosystem at once. Both those things greatly clashed with the lived realities in many projects and companies. I am a happy user of Python 3 today. This migration has also taught me the important lesson not be too stuck on a particular idea. It would have been very easy to pick one of the two sides of that debate. Be stuck on Python 2 (at the risk of forking), or go all in on Python 3 no questions asked. It was the path in between that was quite painful to advocate for, but it was ultimately the right path. I wrote about my lessons of that migration a in 2016 and I think most of this still rings true. That was motivated by even years later people still reaching out to me who did not move to Python 3, hoping for me to embrace their path. Yet Python 3 has changed! Python 3 is a much better language than it was when it first released. It is a great language because it's used by people solving real, messy problems and because it over time found answers for what to do, if you need to have both Python 2 and 3 code in the wild. While the world of Python 2 is largely gone, we are still in a world where Unicode and bytes mix in certain contexts. The Messy Process Fully committing to a single worldview can be easier because you stop questioning everything — you can just go with the flow. Yet truths often reside on both sides. Allowing yourself to walk the careful middle path enables you to learn from multiple perspectives. You will face doubts and open yourself up to vulnerability and uncertainty. The payoff, however, is the ability to question deeply held beliefs and push into the unknown territory where new things can be found. You can arrive at a solution that isn't a complete rejection of any side. There is genuine value in what Rust offers—just as there was real value in what Python 3 set out to accomplish. But the Python 3 of today isn't the Python 3 of those early, ideological debates; it was shaped by a messy, slow, often contentious, yet ultimately productive transition process. I am absolutely sure that in 30 years from now we are going to primarily program in memory safe languages (or the machines will do it for us) in environments where C and C++ prevail. That glimpse of a future I can visualize clearly. The path to there however? That's a different story altogether. It will be hard, it will be impure. Maybe the solution will not even involve Rust at all — who knows. We also have to accept that not everyone is ready for change at the same pace. Forcing adoption when people aren't prepared only causes the pendulum to swing back hard. It's tempting to look for a single authority to declare “the one true way,” but that won't smooth out the inevitable complications. Indeed, those messy, incremental challenges are part of how real progress happens. In the long run, these hard-won refinements tend to produce solutions that benefit all sides—if we’re patient enough to let them take root. The painful and messy transition is here to stay, and that's exactly why, in the end, it works.