Generics aren't ready for Go February 18, 2019 on Drew DeVault's blog

In the distance, a gradual roar begins to grow in volume. A dust cloud is visible over the horizon. As it nears, the shouts of the oncoming angry mob can be heard. Suddenly, it stops, and a brief silence ensues. Then the air is filled with the clackings of hundreds of keyboards, angrily typing the owner’s opinion about generics and Go. The clans of Java, C#, Rust, C++, TypeScript, Haskell, and more - usually mortal enemies - have combined forces to fight in what may become one of the greatest flamewars of our time. And none of them read more than the title of this article before writing their comment.

Have you ever seen someone write something to the effect of “I would use Go, but I need generics”? Perhaps we can infer from this that many of the people who are pining after generics in Go are not, in fact, Go users. Many of them are users of another programming language that does have generics, and they feel that generics are a good fit for this language, and therefore a good fit for any language. The inertia of “what I’m used to” comes to a violent stop when they try to use Go. People affected by this frustration interpret it as a problem with Go, that Go is missing some crucial feature - such as generics. But this lack of features is itself a feature, not a bug.

Go strikes me as one of the most conservative programming languages available today. It’s small and simple, and every detail is carefully thought out. There are very few dusty corners of Go - in large part because Go has fewer corners in general than most programming languages. This is a major factor in Go’s success to date, in my opinion. Nearly all of Go’s features are bulletproof, and in my opinion are among the best implementations of their concepts in our entire industry. Achieving this feat requires having fewer features in total. Contrast this to C++, which has too many footguns to count. You could write a book called “C++: the good parts”, but consider that such a book about Go would just be a book about Go. There’s little room for the bad parts in such a spartan language.

So how should we innovate in Go? Consider the case of dependency management. Go 1.11 shipped with the first version of Go modules, which, in my opinion, is a game changer. I passionately hate $GOPATH, and I thought dep wasn’t much better. dep’s problem is that it took the dependency management ideas that other programming languages have been working with and brought the same ideas to Go. Instead, Go modules took the idea of dependency management and rethought it from first principles, then landed on a much more elegant solution that I think other programming languages will spend the next few years catching up with. I like to make an analogy to physics: dep is like General Relativity or the Standard Model, whereas Go modules are more like the Grand Unified Theory. Go doesn’t settle for anything less when adding features. It’s not a language where liberal experimentation with imperfect ideas is desirable.

I feel that this applies to generics. In my opinion, generics are an imperfect solution to an unsolved problem in computer science. None of the proposals I’ve seen (notably contracts) feel right yet. Some of this is a gut feeling, but there are tangible problems as well. For example, the space of problems they solve intersects with other Go features, which weakens the strength of both features. “Which solution do I use to this problem” is a question which different people will answer differently, and consequently their code at best won’t agree on what “idiomatic” means and at worst will be simply incompatible. Another problem is that the proposal changes the meaning of idiomatic Go in the first place - suddenly huge swaths of the Go code, including the standard library, will become unidiomatic. One of Go’s greatest strengths is that code written 5 years ago is still idiomatic. It’s almost impossible to write unidiomatic Go code at all.

I used to sneer at the Go maintainers alongside everyone else whenever they’d punt on generics. With so many people pining after it, why haven’t they seen sense yet? How can they know better than all of these people? My tune changed once I started to use Go more seriously, and now I admire their restraint. Part of this is an evolution of my values as a programmer in general: simplicity and elegance are now the principles I optimize for, even if it means certain classes of programs are simply not on the table. And I think Go should be comfortable not being suitable for writing certain classes of programs. I don’t think programming languages should compete with each other in an attempt to become the perfect solution to every problem. This is impossible, and attempts will just create a messy kitchen sink that solves every problem poorly.

Nina Tucker from Fullmetal Alchemist

fig. 1: the result of C++'s attempt to solve all problems

The constraints imposed by the lack of generics (and other things Go lacks) breed creativity. If you’re fighting Go’s lack of generics trying to do something Your Way, you might want to step back and consider a solution to the problem which embraces the limitations of Go instead. Often when I do this the new solution is a much better design.

So it’s my hope that Go will hold out until the right solution presents itself, and it hasn’t yet. Rushing into it to appease the unwashed masses is a bad idea. There are other good programming languages - use them! I personally use a wide variety of programming languages, and though I love Go dearly, it probably only comes in 3rd or 4th place in terms of how frequently it appears in my projects. It’s excellent in its domain and doesn’t need to awkwardly stumble into others.

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