I was pointed to the Odin language after my post about the Zig language. On the surface, Odin and Zig are very similar, but they have some fundamental differences in behavior and mindset. I’m basing most of what I’m writing here on admittedly cursory reading of the Odin language docs and this blog post.
Odin has a great point on conditional compilation. The if statements that are evaluated at compile time are hard to distinguish. I like Odin’s when clauses better, but Zig has comptime if as well, which make it easier. The actual problem I have with this model in Zig is that it is easy to get to a situation where you write (new) code that doesn’t get called, but Zig will detect that it is unused and not bother compiling it. When you are actually trying to use it, you’ll hit a lot of compilation errors that you need to fix. This is in contrast to the way I would usually work, which is to almost always have the code in compliable state and leaning hard on the compiler to double check my work.
Beyond that, I have grave disagreements with Ginger, the author of the blog post and the Odin language. I want to pull just a couple of what I think are the most important points from that post:
I have never had a program cause a system to run out of memory in real software (other than artificial stress tests). If you are working in a low-memory environment, you should be extremely aware of its limitations and plan accordingly. If you are a desktop machine and run out of memory, don’t try to recover from the panic, quit the program or even shut-down the computer. As for other machinery, plan accordingly!
This is in relation to automatic heap allocations (which can fail, which will usually kill the process because there is no good way to report it). My reaction to that is “640KB is enough for everything”, right?
To start with, I write databases for a living. I run my code on containers with 128MB when the user uses a database that is 100s of GB in size. Even if running on proper server machines, I almost always have to deal with datasets that are bigger than memory. Running out of memory happens to us pretty much every single time we start the program. And handling this scenario robustly is important to building system software. In this case, planning accordingly in my view is not using a language that can put me in a hole. This is not theoretical, that is real scenario that we have to deal with.
The biggest turnoff for me, however, was this statement on errors:
…my issue with exception-based/exception-like errors is not the syntax but how they encourage error propagation. This encouragement promotes a culture of pass the error up the stack for “someone else” to handle the error. I hate this culture and I do not want to encourage it at the language level. Handle errors there and then and don’t pass them up the stack. You make your mess; you clean it.
I didn’t really know how to answer that at first. There are so many cases where that doesn’t even make sense that it isn’t even funny. Consider a scenario where I need to call a service that would compute some value for me. I’m doing that as gRPC over TCP + SSL. Let me count the number of errors that can happen here, shall we?
- Bad reaction on the service (run out of memory, for example).
- Argument passed is not a valid one
- Invalid SSL certificate
- Authentication issues
- TCP firewall issue
- DNS issue
- Wrong URL / port
My code, which is calling the service, need to be able to handle any / all of those. And probably quite a few more that I didn’t account for. Trying to build something like that is onerous, fragile and doesn’t really work. For that matter, if I passed the wrong URL for the service, what is the code that is doing the gRPC call supposed to do but bubble the error up? If the DNS is returning an error, or there is a certificate issue, how do you clean it up? The only reasonable thing to do is to give as much context as possible and raise the error to the caller.
When building robust software, bubbling it up so the caller can decide what to do isn’t about passing the back, it is a b best practice. You only need to look at Erlang and how applications with the highest requirements for reliability are structured. They are meant to fail, error handling and recovery is something that happens in dedicated (supervisors) locations, because these places has the right context to make an actual determination.
The killer impact of this, however, is that Zig has explicit notion of errors, while Odin relies on the multiple return values system. We have seen how good that is with Go. In fact, one of the most common issues with Go is the issue with how much manual work it takes to do proper error handling.
But I think that the key issue here is that errors as a first class aspect of the language gives us a very powerful ability, errdefer. This single language feature is the reason I think that Zig is an amazing language. The concept of first class errors combine with errdefer makes building complex structures so much easier.
Consider the following code:
Note that I’m opening a file, mapping it to memory, validating its size and then that it has the right hash. I’m using defer to ensure that I cleanup the file handle, but what about the returned memory, in this case, I want to clean it up if there is an error, but not otherwise.
Consider how you would write this code without errdefer. I would have to add the “close the map” portion to both places where I want to return an error. And what happens if I’m using more than a couple of resources, I may be needing to do something that require a file, network socket, memory, etc. Any of those operations can fail, but I want to clean them up only on failure. Otherwise, I need to return them to my caller. Using errdefer (which relies on the explicit distinction between regular returns and errors) will ensure that I don’t have a problem. Everything works, and the amount of state that I have to keep in my head is greatly reduce.
Consider how you’ll that that in Odin or Go, on the other hand, and you can see how error handling become a big beast. Having explicit language support to assist in that is really nice.