A tale of two Rusts

Posted on Sat 24 December 2016 in Programming • Tagged with Rust, nightly Rust, stable Rust, Rocket.rsLeave a comment

The writing has been on the wall for many months now, but I think the time has come when we can officially declare it.

Stable Rust is dead. Nightly Rust is the only Rust.

Say what?

If you’re out of the loop, Rust is this newfangled system programming language. Rust is meant to fit in the niches normally occupied by C, so its domain includes performance-sensitive and safety-critical applications. Embedded programming, OS kernels, databases, servers, and similar low-level pieces of computing and networking infrastructure are all within its purview.

Of course, this “replacing C” thing is still an ambition that’s years or decades away. But in theory, there is nothing preventing it from happening. The main thing Rust would need here is time: time to buy trust of developers by having been used in real-world, production scenarios without issues.

To facilitate this (and for other reasons), Rust has been using three release channels with varying frequency of updates. There are the stable, beta, and nightly Rust. Of those, beta is pretty much an RC for a future stable release, so there aren’t many differences at all between the first two channels.

Nightly perks

This cannot be said about nightly.

In fact, nightly Rust is essentially its own language.

First, there is a number of exclusive language features that are only available on nightly. They are all guarded by numerous #![feature(...)] gates which are required to activate them. Because stable Rust doesn’t accept any such directive, trying to compile code that uses them will fail on a non-nightly compiler.

This has been justified as a necessary step for testing out new features in real scenarios, or at least those that resemble (stable) reality as close as possible. Indeed, many features did eventually land in stable Rust by going through this route — a recent example would be the ? operator, an error-handling measure analogous to the try! macro.

But some features take a lot of time to stabilize. And few (like zero_one which guards the numeric traits Zero and One) may even be deprecated without ever getting out of the nightly channel.


Secondly, and most importantly, there is at least one feature that won’t get stabilized ever:


And it’s all by design.

This plugin switch is what’s necessary to include #![plugin(...)] directives. Those in turn activate compiler plugins: user-provided additions to the compiler itself. Plugins operate against the API provided directly by rustc and enhance its capabilities beyond what the language normally provides.

Although it sounds rather ominous, the vast majority of plugins in the wild serve a singular purpose: code generation. They are written with the sole purpose of combating Rust’s rigidity, including the (perfectly expected) lack of dynamic runtime capabilities and the (disappointingly) stiff limits of its wanting macro system.

This is how they are utilized by Diesel, for example, a popular ORM and SQL query interface; or Serde, a serialization framework.

Why compiler plugins can never be stable, though? It’s because the internal API they are coded against goes too deep into the compiler bowels to ever get stabilized. If it were, it would severely limit the ability to further develop the language without significant breakage of the established plugins.


Wait,” you may ask, “how do we even talk about «established» compiler plugins? Shouldn’t they be, by their very definition, unstable?”

Well… yes. They definitely should. And therein lies the crux of the problem.

Turns out, plugins & nightly Rust are only mostly treated as unstable.

In reality, the comfort and convenience provided by nightly versions of many libraries — all of which rely on compiler plugins — is difficult to overstate. While their stable approximations are available, they at best require rather complicated setup.

What’s always involved is a custom build step, and usually a separate file for the relevant code symbols and declarations. In the end, we get a bunch of autogenerated modules whose prior non-existence during development may also confuse IDEs and autocompletion tools.

For all those reasons and more, an ecosystem has developed where several popular libraries are “nightly but pseudo-stable”. This includes some key components in many serious applications, like the aforementioned ORM & serialization crates.

The precedent

And so has been the state of affairs until very recently. The nightly Rust has been offering some extremely enticing features, but the stable channel was at least paid a lip service to. However, the mentality among library authors that “nightly-first” is an acceptable policy had been strong for a long time now.

No wonder it has finally shifted towards “nightly-only”.

Meet Rocket, the latest contestant in the already rich lineup of Rust web frameworks. Everything about it is really slick: a flashy designer website; approachable and comprehensive documentation; and concise, Flask-like API for routing and response handling. Predictably, it’s been making quite a buzz on Reddit and elsewhere.

There is just an itty bitty little problem: Rocket only works on nightly. No alternatives, no codegen shims… and no prospects of any change in the foreseeable future. Yet, there doesn’t seem to be many people concerned about this, so clearly this is (a new?) norm.

The Rusts split

In essence, Rust is now two separate languages.

The stable-nightly divide has essentially evolved into something that closely resembles the early stages of the 2.x vs. 3.x split in the Python world. The people still “stuck” on 2.7 (i.e. stable) were “holdouts”, and the future was with 3.x (nightly). Sure, there have been some pithy backports (feature stabilizations), but the interesting stuff has been happening on the other side.

It’s astonishing that Rust managed to replicate this phenomenon without any major version bumps, and with no backwards-incompatible releases. Technically, everything is still version 1.x.. Not even Cargo, the Rust package manager, recognizes the stable-nightly distinction.

But that’s hardly any consolation when you try to install a nightly-only crate on stable Rust. You will download it just fine, and get all the way to compiling its code, only to have it error out due to unsupported #![feature(...)] declarations.

What now?

The natural question is, can this situation be effectively addressed?

I hope it’s obvious why stable Rust cannot suddenly start supporting compiler plugins. Given that they rely on rustc internals which aren’t standardized, doing so would be contrary to the very definition of a “stable” release channel.

The other option is to fully embrace nightly as de facto recommended toolchain. This has been informally happening already, despite the contrary recommendations in the official docs.

The downsides are obvious here, though: nightly Rust is not a misnomer at all. The compiler is in active development and its build breaks often. Some of those breakages make it into nightly releases with unsatisfying regularity.

Of course, there was also another option: stick to the intended purpose of release channels and don’t build castles on the sand by publishing nightly-first or nightly-only crates. This ship seems to have sailed by now, as the community has collectively decided otherwise.

Oh well.

It’s just a little ironic that in a language that is so focused on safety, everyone is perfectly happy with an unstable compiler.

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Please don’t use Click

Posted on Fri 20 May 2016 in Programming • Tagged with Python, CLI, UI, ClickLeave a comment

…not for standalone programs anyway.

Chances are, you have written some command line programs in Python. This is quite probable even if you normally code in some other language. And if you have, it is not unlikely that you needed to parse the argv of your program at one point or another.

There are plenty of options here, both in the standard library as well as among third party packages. One does stand out, however, and it’s mostly for how it is often overused. I’m talking about Click here.

If you wanted to use it in your next Python program, I hereby urge you to reconsider.

What’s the fuss?

click_ The somewhat bizarrely named Click library is described as a “package for creating beautiful command line interfaces”. Its main trick is the ability to create subcommands by adorning Python functions with the @click.command() decorator1. It then makes them coalesce into an argument parser, equipped with the necessary dispatching logic.

This idea isn’t new, of course. Prior art goes back at least seven years to the now-abandoned opster package. Click, however, was the first one of its kind to garner noticeable popularity, which is easily attributed to whom it’s been authored by.

So while my arguments against using this kind of CLI framework would apply to any package implementing the paradigm, it just happens that Click is currently its most prominent example. Purely for the sake of convenience, I will therefore refer to it as if it was interchangeable with the whole concept. Because why not? Whatever you may say about the library’s name, it’s hard to imagine a more concise moniker than a simple Click.

What’s wrong, then, with the way Click handles command line interfaces?

CLI: Little Interfaces

It’s how it encourages to treat them as an accidental afterthought rather than a deliberate design decision.

For applications invoked repeatedly from a terminal, their command line arguments and flags are the primary means of user interaction2. It is how users communicate their intent to perform an action; provide the neccessary input data to carry it throgh; decide how they want to receive the output; and control many other aspects of the programs execution. Absent graphical components and widgets, the command line is virtually the only way to interact with a terminal program.

In other words, it is the UI.

And how important the UI is for any application? It seems to be important enough that entire fields of study are devoted to reducing friction of human-computer interaction. In many projects, the emphasis on user interface design is on par with that of actual software engineering.
Like everything, of course, it is susceptible to trends and fads (such as the recent “mobile/responsive everything!” craze). But its significance remains undiminished. Quite the opposite: in the age of ubiquitous computing, user interfaces are probably more important than ever.

Yes, this includes CLI. One of the main reasons we turn to the command line are speed and efficacy. Common tasks must utilize short and convenient syntax that is quick to integrate into user’s muscle memory. Others should not only be possible, but discoverable and accessible without going through reams of man pages.

Any terminal program intended for frequent use by humans should therefore strive to excel in those two qualities. But except for the simplest of cases, it won’t happen by itself. Designing an efficient CLI for any non-trivial application is a challenging and demanding task.

It doesn’t click

With Click, however, we’re encouraged to just wing it.

Click tells us to slap some decorators on our top-level functions and call it a day. Sure, you can dig deep enough and uncover the underlying layers of abstraction that may eventually allow you do things for which argparse has a first-class support.

By default, however, Click shoehorns your programs into predefined patterns that, incidentally, mirror those of some least intuitive command-line tools in existence.

Indeed, the whole idea of subdiving your program into several distinct is already suspect, for it appears at odds with the fundamental Unix philosophy of doing one thing well. While it is occasionally justified, it shouldn’t be the first thing that comes to your mind. But that’s completely at odds with the Click’s approach, where not ending up with multiple distinct commands is something you have to consciously avoid.

…though it sometimes might

So, what am I suggesting you use instead libraries such as Click?… Nothing outrageous, really.

If you care about your command line interface, consider just using the argparse module. Yes, it will force you to create parser objects, add arguments & flags to it, and in general pay some attention to the whole business. When it comes to UI, it’s always good to make it an explicit concern, maybe even sufficient to warrant its own module.

Alternatively, the docopt library provides another take on the UI-first approach to CLI, though it is more limited in its capabilities3.

Finally, I’m not advocating to ditch Click in all scenarios. There’s plenty of situations when we’re interested in getting any CLI up and running, and not so much in making the most efficient and intuitive interface possible. The prime example is any kind of automation scripts that are ancillary to some bigger project, like manage.py is in Django4. The Python ecosystem doesn’t really have dedicated task runners that are as featureful as Grunt or Gulp, and that makes Click a viable and compelling option5.

But for standalone programs whose CLI is the main interface? Yeah, not really.

  1. Oddly enough, that pair of parentheses seems to be mandatory. 

  2. Environment variables and config files deserve a honorary mention, of course. But those are usually derivatives of the command line arguments, containing e.g. the default values for flags. 

  3. Click’s own documentation actually describes quite nicely how theirs and docopt’s philosophies differ in a way that’s consistent with this article. 

  4. Incidentally, this appears to be a major motivation behind creating Click in the first place: to support web applications built upon on the Flask framework, and possibly obviate the need for extensions such as Flask-Script

  5. This saying, there are some task runners which offer similar experience, like Invoke

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Package managers’ appreciation day

Posted on Sat 26 March 2016 in Programming • Tagged with packages, package manager, node.js, npm, C++Leave a comment

By now you have probably heard about the infamous “npm-gate” that swept through the developer community over the last week. It has been brought up, discussed, covered, meta-discussed, satirized, and even featured by some mainstream media. Evidently the nerds have managed to stir up some serious trouble again, and it only took them 11 lines of that strange thing they call “code”.

No good things in small packages

When looking for a culprit, the one party that everyone pounced on immediately was of course the npm itself. With its myriad of packages that could each fit in a tweet, it invites to create the exact house of cards we’ve seen collapse.

This serves as a good wake-up call, of course. But it also compels to throw the baby out with the bathwater, and draw a conclusion that may be a little too far-fetched. Like perhaps declaring the entire idea of managing dependencies “the npm way” suspect. If packages tend to degenerate into something as ludicrous as isArray — to say nothing of left-pad, which started the whole debacle — then maybe this approach to software reusability has simply bankrupted itself?

A world without *pm

I’m right away responding to that with a resounding “No!”. Package management as a concept is not responsible for the poor decision making of one specific developer collective. And anyone who might think tools like npm do more harm than good I ask: have you recently written any C++?

See, C++ is the odd one among languages that at least pretend to be keeping up with the times. It doesn’t present a package management story at all. That’s right — the C++ “ecosystem”, as it stands now, has:

  • no package manager
  • no repository of packages
  • no unified way of managing dependencies
  • no way to isolate development environments of different projects from one another

Adding any kind of third-party dependency to a C++ project — especially a portable one, which is allegedly one of C++’s strengths — is a considerable pain, even when it doesn’t require any additional libraries by itself. And environment isolation? Some people are using Linux containers (!) for this, which is like dealing with a mosquito by shooting it with a howitzer.

Billions upon billions of lines
To build a C++ binary, you must first build the userspace.

But hey, at least they can use apt-get, right?…

So, string padding incidents aside, package managers are absolutely essential. Sure, we can and should discuss the merits of their particular flavors and implementation details —like whether it’s prudent to allow “delisting” of packages. As a whole, however, package managers deserve recognition as a crucial part of modern language tooling that we cannot really do without.

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You Don’t Have to Interview like Google

Posted on Mon 28 December 2015 in Programming • Tagged with Google, interviews, startups, career, hiringLeave a comment

If you look at discussion forums for people in the CS industry — like /r/cscareequestions or even just Hacker News — you’ll find lots of talk about the so called Big Four companies.

This is mostly in the context of applying to them, or going through their interview process. Which of the large software corporations are discussed here tends to fluctuate a little bit, but both Google and Microsoft are invariably included, with Facebook popping up more often than not.

Because of their privileged positions as very desirable places to work, these companies tend to be taken as models for others to mimic1. Probably the most apparent and direct outcome is the increasing prevalence of “Google-style” interviews, which are now utilized by countless software shops around the world.

Whiteboard coding is how they are often called. It is a subject of an intense debate, whether or not they “work”, and adequately assess the engineering aptitude of candidates. If some high profile anecdotes are of any indication, the most common complaint is that they fail to recognize competence by ignoring previous professional work, open source contributions, conference talks, and so on.

Instead, the whiteboard interview requires demand showing a “pure” problem solving ability within a relatively short time window, all without some broader context or even the usual tools of the trade: laptop, editor, and a search engine.

As a Googler who had gone through this process and has now conducted a few of those interviews himself, I find those complaints mostly valid albeit misdirected.

The problem isn’t really that Google interviews like it does.

What’s really the issue is other companies implementing the same process, and not realizing it cannot possibly work for them.

Somewhat special

It is important to understand that Google’s stance on interviewing is influenced by some unique circumstances:

  • very high and steady influx of potential candidates

  • comparatively long tenure of the average engineer and the general focus on employee retention

  • huge and mostly proprietary software stack working at a scale that almost no others do

From this perspective, it makes sense to utilize cautious hiring strategies that may result in a high ratio of false negatives2. When rejections are cheap but the new hires are supposed to be here for the long run — partially because of the long ramp-up time necessary to become productive — it can be costly to give candidates the benefit of the doubt.

The last point also explains why proficiency with specific technologies is less useful than general flexibility grounded in strong fundamentals. To put it shortly, Google prefers you know CS rather than CSS.

Finally, whiteboard coding is just one input to the evaluation process, but it tends to be the most trustworthy one. Besides programming aptitude, the ideal candidate would show a proven track record of technical leadership while tackling complex problems that span a broad scope.
Unfortunately, those qualities are difficult to convey efficiently and reliably through the usual industry channels: a resume, references from previous jobs, GitHub profile, etc.

Different conditions

Given the above reasoning as to why “Google-style” interviews seem to work well for Google, I hope it’s evident why they are likely a poor choice for companies that don’t share the same characteristics as the Big 4.

For one, it is highly unusual for a software shop in today’s market to command a sizeable pool for qualified candidates. Software engineering vacancies often go unfilled for weeks and months, even if the company isn’t exactly looking for “rockstars”, “ninjas”, “gunslingers”, or whatever the silly term du jour is. Those who meet the requirements usually have their pick at many different offers, too.

The reality for many companies (especially startups) is also one where they are unable or unwilling to invest much in the retention of their employees. Because the employment relationship in this industry tends to be quite volatile (which isn’t necessarily a bad thing), it often makes sense for companies to look for a near-immediate payoff when hiring.

We owe it to the prevalent open source technologies that this isn’t entirely unreasonable. If your software stack is composed entirely of components that are available in the open, you can probably find engineers who are familiar with most of them. They can be productive members of your team almost literally from day one!

Right tool for the job

The most important observation is that every company is different, and following the One True Best Practice™ will likely prevent you from utilizing the best qualities of your work place. Smaller shops, for example, could take a more personalized approach to hiring: let candidates actually sit with engineers, solve real-life problems, and have deep technical conversations.

Of course, you may still find whiteboard coding valuable in its own right. Indeed, a simple test for at least the basic programming skill appears to be a necessary sanity check.

But a full suite of difficult technical interviews with tough algorithmic problems that last a better part of the day? Most likely not.

  1. Some seem to have succeeded to such an extent that you may occasionally hear about “Big N”. This often includes some currently large and/or successful but still “hip” startups. IT is such a fashion industry sometimes… 

  2. Though on the flip side, it exacerbates the impostor syndrome among people who do get hired, as their success could easily be construed as mostly luck. 

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Don’t Copy & Paste. Retype.

Posted on Sat 03 October 2015 in Programming • Tagged with problem solving, Stack Overflow, typingLeave a comment

In this day and age, Google and Stack Overflow are quite essential tools for any developer. Lately, though, the latter seems to be getting some bad rap. On one side, it’s because of seemingly peculiar and sometimes alienating moderation policies. But more pertinently, it’s the apparent rise of a phenomenon that’s wittily dubbed “the full Stack Overflow developer“.

In a nutshell, individuals deserving to be called that are code slingers who throw software artifacts together mostly by copying and pasting code samples found in Stack Overflow answers. They may be getting something working pretty quickly, but they also lack understanding of problems they’re facing and solutions they’re using so cheerily.

Of course, not every instance of code Copy Pasta is to be scorned. I’m pretty sure most people reading this post (and certainly the person writing it!) are guilty of replicating at least a few snippets from Stack Overflow, verbatim, in their own codebase. Heck, we may have even done so with nigh zero interest as to why it has been written this way. Not every technology is intrinsically fascinating, after all, and deadlines are sometimes too close for comfort.

But if so, does it mean we are gradually turning into full Stack Overflow developers?… Yikes! Surely we don’t want that to happen!

Mitigation tactic

Before you shut off your Internet connection altogether while coding, consider employing the following technique whenever you feel like scraping a piece of code from Stack Overflow, and dumping it in your project source.

Don’t use the clipboard. Don’t copy and paste. Retype the code you’ve found instead.

It’s going to take more time, yes. It’s definitely more cumbersome than just hitting Ctrl+C/Ctrl+V. It may also make little sense: if the end result is the same, why does it matter whether the code was transfered through the clipboard or not?


I’d argue, however, that it makes perfect sense. From the least to the most important, the reasons why I think so are the following:

  • The fact that retyping is slower than copy-pasting is what actually makes it better. If you vow not to use the clipboard, you’re much less likely to just pick whatever’s the first Stack Overflow result Google has given. You’ll weigh different solutions, and you’ll be rightfully biased towards shorter and simpler ones.

  • When you type something, you cannot do it completely thoughtlessly. Whether you want it or not, you’ll absorb some of the knowledge through sheer osmosis, because the code will flow through your eyes and fingers as it’s transfered from the browser to your editor or IDE. Your subconscious brain will latch onto the bits and pieces of information, and it will sort them out for you to use later. Even if you didn’t intend to, you will most likely learn something.

  • But most importantly, what you type almost certainly won’t be a perfect copy of the original snippet. As you progress through the code, you’ll inevitably deviate from it, if only to conform to a particular style guide your project is following.
    It’s quite likely, though, that you’ll make larger changes as well. You will replace familiar patterns with calls to utility functions. You’ll rearrange the code visually for better readability. You will add comments, or extract functions to make it more self-documenting. You might even enhance and customize it, so that you can abstract and reuse it multiple times.

Afterwards, what you’ve just typed won’t be just some code you have found on the Internet. It’ll be your code.

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