Assessing Abstractions

July 2020

Some abstractions are ticking time bombs, while others help you move fast. How can you tell? What follows is my personal exploration for how I assess abstractions.

Problem

We add abstractions in our programs to solve problems. So, let’s start with the fundamental value proposition: what problem does our abstraction solve?

Let’s take a look at one example abstraction:

NLP.parse(...) // => { intent: "set_alarm", at: "1593538633430" }

This could be a natural language processing abstraction, which lets us take a piece of text, and extract meaning from it. The inherent problem of natural language processing is pretty darn complex, so an abstraction that helps us solve it would be very valuable. This is a sign of a good abstraction.

Now let’s compare that to

StringSplitter.easySplit(str, splitStr)

Maybe this abstraction, adds a light layer on top of string.split. For example, it may make it so you don’t have to worry about regexes, and can turn common string patterns into regexes. The value of a StringSplitter abstraction is pretty darn low. Maybe StringSplitter treats splitStr in a way that’s a bit more in-line with the someone’s thinking, but at the end of the day this boils down to an indirection.

This leads us to the first principle. The more complex the problem it solves for you, the better the abstraction (1).

Interface

After we’re convinced that the abstraction we are about to add solves a tough problem for us, the next thing to consider is the interface: how do we interact with the abstraction? Imagine if NLP.parse was called like this:

NLP.parse(lang, text)

This is a great interface. It’s small. We don’t need to understand any internals. For the main use-case, all we need to do is to provide language and text. Compare that with

NLP.parse(
  text,
  lang, 
  strategy,
  shouldUseFlagA,
  ...
  shouldUseFlagZ
)

In order to use this version, we’d need to deeply understand the internals of NLP.parse. This lowers the value of the abstraction, because we need to do more work to solve the same level of complexity.

This leads us to the second principle: great abstractions have small interfaces.

Breakthrough Cost

Now that we have an abstraction with a simple interface that solves a hard problem, we need to ask a possibly fatal question: what happens when we need to break through the abstraction?

All abstractions are leaky at some point. What will happen when you need the abstraction to behave differently? What will happen when it doesn’t work as you expect?

For example, for NLP.parse(lang, text), what if we needed to sort and score the results differently? What if there’s a bug, and we aren’t getting the entity we expect, can we look through and debug?

Understanding the answer to this, will give us the breakthrough cost. To do this, we need to peak through the code. How is NLP.parse implemented?

parse(lang, text) { 
  return format(scoreEntities(fetchEntities(lang, text)))
}

In one solution, it could be composed of other abstractions that we can take advantage of. This is a great sign, because we can reuse the underlying abstractions in cases where we need to do something more complicated. Compare that to

parse(lang, text) { 
  internalParse(lang, text, flagA, flagB, ...flagZ)
}

This feels more dangerous. If these flags all head to the same function, it’s a sign that a bunch of different features are complected together. It’s also worrying: what if one of these flags don’t do what you want? you may have to fork the abstraction.

This leads us to the third principle: great abstractions are transparent. I think this principle is the most overlooked. It’s easy to take the productivity win upfront, but if the abstraction you add can’t be changed, and can’t be introspected, it’s very likely to bite you at some point.

Generality

The final principle is orthogonal to the last three, but maybe it’s the most important. Hardy said there is no permanent place in the world for ugly mathematics — So it is with abstractions. The beauty in math relates to how “general” and “tight” the solution is. I think this parallels well with abstractions.

If you use an abstraction that is “essentially” simpler, it’s more likely to last, and it’s likely to be more powerful.

Consider if the abstraction for NLP, was made up of specific algorithms, just for natural language processing. This would still be very valuable, but what would be even more valuable, is if the abstractions that this library was composed of was more general: if the parts that compose it were deep learning abstractions, you could reuse them for other problems.

Fin

And we reach the end. To pick great abstractions: pick the ones that solve a complex problem for you. Make sure they have a simple interface, and take a look at the internals, so you’re confident you can jig things up if needed. The more general and simple you can get for the same amount of power, the better.

Want to see some great abstractions in the wild? First, chances are you are using many of them: TCP, higher order functions like map & filter, React. Some you may not have explored: Go’s CSP, Rich Hickey’s Datomic, or his seq abstraction in Clojure. As you pick up abstractions, I encourage you to run each one as an experiment: ask yourself at the end how things went, discuss them with your friends, and soon you’ll develop a much more nuanced taste.

(1) The rabbit hole gets deeper. Even if an abstraction solves a complex problem you have, you may need to take a step back and also ask: why do I have this problem? For example, kubernetes may be a great solution to building distributed systems, but why do you have a distributed systems problem? Many times the problem itself can be avoided. For the answer to that, Hacker’s Paradise tries to covers it.

Thanks to Alex Reichert, Daniel Woelfel, Martin Raison, Sean Grove for reviewing drafts of this essay