Retrofitting null-safety onto Java at Meta

Programmers want to deliver working code. If that code needs to be asynchronous and handle data, they'll use whatever is easy, acceptable and available to use with their language. That "feature" may be provided by the language, by a compiler, by IDE code generation, by a pre-processor, by a post-processor, by runtime code generation or by a library that is using some idioms.

Most programmers (my educated guess is 80%) don't care very much how they get that done, as long as they can get quickly learn it and get stuff done keep their managers and co-workers are happy. Programmers need to go through a learning curve to learn new features, whether they are library features or language features. A language can "cheat" a little by keeping itself lean and mean and deliver data class creation to IDEs and annotation processors, while letting libraries implement concurrency and even coroutines (see Quasar for Java and Greenlet for Python).

This doesn't remove any complexity from the programmer dealing with these languages. Some times it could make the programmers' life even more miserable since there are multiple competing methods to choose from.

Having led programmer teams working in both C# and Java, I can clearly say that C# programmers are less confused by data classes and concurrency issues. I wouldn't say C# is perfect (C# properties are messy and their async/await implementation is pioneering, but somewhat confusing). I don't like all features that get added to C# either, and I sometimes think Microsoft could exhibit more care here. But I feel less "burdened" when we have to use C# (or Kotlin, Go or to certain degree Rust) for concurrency and asynchronous I/O rather than using Java and JavaScript, which have way too many historical ways of doing the same thing.

I think you're thinking too much from the perspective of a _language developer_. Language developers like less complexity in their languages, and that's totally understandable. But developers don't care so much about that, and despite what you say, I don't think there's good evidence that this is what makes a language extremely successful. The process of a language becoming successful is a lot more complicated than that and I doubt if it can be easily described. After all, the historical data we've got is too sparse. But if we look at languages that did become successful before and after Java, most of them were quite complex compared to their competitors:

PL/I was considered extremely complex and bloated in its time, but it became popular nevertheless, since it had a strong corporate backing from IBM. The very same company, incidentally, was one of the largest corporate backers of Java since the early 1990s.

While C was arguably almost as lean as Pascal (if not as easy to learn), it barely got any foothold in the world where Java has won so decisively later: Enterprise line-of-business software. These programs tended to be written mostly in COBOL and PL/I on mainframes, and on the PC developers used whatever was available, including assembly. Smalltalk (not a "simple" language for its time, considering the _entire_ package you'd get) also had a short heyday. But when Java came out, the world settled on C++. Sure, C++ back then was less than the shining paragon of feature creep that it is today, but it was still a rather complex language. The various dialsects of object-oriented Pascal were simpler. Modula 3 was simpler. Smalltalk was probably simpler too. But C++ won.

In the defense industry during the 1980s, Ada was queen. The reasons for this are really simple: this was often what the DoD mandated. Just like many corporate IT departments mandated Java years later. Anecdotally, all Ada programmers I met loved the language back then. They didn't lament the massive amount of features (for the time).

Embedded languages are also an interesting case. Small languages like Lua are quick objectively easier to embed and you'd think they'll win decisively. Lua is quite popular as an embedded language, but it seems to be on par with Python and losing to JavaScript.

Why did JavaScript become so popular? It's certainly not a simple language. There are many complex features that are not used very often like proxies, generators and all the various Object functions. There are often several layers of historical cruft or different solution strategies, such as prototypes vs. Object.create() vs. classes. Or "Error(...)" vs. "new Error(...)" or var vs. let. Or this-binding arrow functions vs. traditional anonymous functions and Function.prototype.bind(). Equality laws type coercion are famous bonkers[1]. Even from its very inception, JavaScript was more complex than necessary, and made some decisions that kept annoying generations of developers (e.g. vars and prototypes). And it still won, since Brendan Eich got included in Netscape and Microsoft rushed to copy it with (the frustratingly randomly incompatible) JScript. JavaScript never made developers happy and still has a certain type of fatigue named after it.

> the objective fact is that no language with a strategy of adding features quickly has performed better in the market than Java

This is deductive reasoning from a single datum, where there are many other social and technological factor that could determine language success. The fact is that before Java, the most successful languages - especially in the same industry Java rules most strongly today (business programs) - have been rather complex: COBOL, PL/I, C++. And to the best of my knowledge, they all had strategy of indiscriminately adding features in the language level.

I fail to see any strong evidence to your claim, while there is some anecdotal evidence to the contrary.

>> But I disagree with the stance that stackful coroutines are superior. > Okay. There aren't many things all developers agree on.

That's great, but then it's just opinion. I personally prefer stackless coroutines, but I won't go ahead say they're strictly superior to stackless coroutines. There's a reason many languages still chose to go with stackless coroutines even though stackful coroutines are far from new. Swift has added async await quite recently an I'm pretty sure Apple was fully aware of the work done on Project Loom, Go, Lua, Erlang and many others. Microsoft could have very well chosen stackful coroutines for C# and implemented them to be transparent like virtual threads. gevent was doing the same thing (in a more primitive way) in Python after all. It's not like stackful coroutines are a new kind of tecnology we had to sit and wait for years to research properly.

[1] https://www.destroyallsoftware.com/talks/wat

1) an empty list/array 2) throw an exception if the return value is missing. 3) -1

Optional can be used as a better alternative in all these cases. It's not just null.

I'm not really arguing for that. I'm really not advocating any school of language design here. I'm just saying that from the point of view of _the users_ the actual purity of the core language matters less than the state of the ecosystem.

I'm perfectly happy with the current course of Java, especially post Java 8. It just isn't for me, and I wouldn't use it or recommend using it for most types of software I'm dealing with. I can say the exactly same for C++.

There's a place for conservative and highly selective languages like Java, C and Go. As a CTO or a tech lead I generally tend to avoid these languages and I don't think they work great for my organization, but they might work out for other people. It's good to have choice. And it goes both way: if you need to stay within the JVM and you're not satisfied with Java, you've got Scala, Kotlin and Clojure. Between them, thy cover a lot of ground and have very different strategies for adding features.

The most conservative users of Java have their choice though. They don't care very much about the absolute _size_ of the language, but they very much dislike change. And for these businesses, the current pace Java is moving at is still too fast. That's why we still have a great deal of businesses out there running Java 8 with outdated frameworks and libraries. But they're not unhappy with Java, since they could always stay at an older version - and that's exactly what they do.

> I disagree. C was still more popular than C++ in the nineties

I was talking specifically about the industry which is now dominated by Java: business software. C++ strongly dominated two industries throughout the 90s: post-mainframe business software of all kinds and desktop GUI software. C never came close to dominating business software. On the early days of the desktop these were often written in Basic or Pascal and by the 1990s C++ became the standard object oriented language, although most of its competitors were simpler. C was probably dominant in early desktop GUI software, but was completely replaced[1] by C++ and other languages by the mid-1990s. C was still dominant in games throughout the 1990s, although C++ would come to dominate this industry later on.

> and compared to the average of the time, COBOL was simpler than C#.

I disagree that COBOL was simpler than earlier languages like FORTRAN or LISP, or contemporaries like ALGOL 60, but it's probably a moot point. COBOL was not a general-purpose language at that point, and it's structure was quite unique.

> But even that doesn't matter. Teachers are telling us that if we increase the pace, even more of them would switch to teaching Python.

I'm a bit surprised by this sentiment, since Python has been steadily adding major features since its very inception, while Java only increased its pace rather recntly, starting with Java 9. Python started gaining popularity as a teaching language during the priod it was moving faster than Java.

> It's not as simple as that. Implementing user-mode threads is drastically more difficult than async/await.

I completely agree with you here. This must have been a major part of the .NET team's rationale. But they could have undertaken a multi-year project to implement it like you did. The end-result probably would have been the same: a variety of community-based projects that try to bring async I/O and M:N concurrency to the language.

[1] Outside of small holdouts like Gtk and Carbon I guess.