Discussion on: What is an abstraction?

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Eric Normand Author

Hey Kasey,

Yeah, great examples.

We tend to call those things "abstraction". And they are in the Sussman sense since we're naming a compound element. But it's not an abstraction in the Dijkstra sense, because it's not really making it so you can be totally precise. Or at least it's hard to make it precise. You're telling the user of your library that they can subclass this thing but they have to follow all of these poorly-defined rules. To make it less leaky, you should be able to limit the number of rules you have to follow, or at least make them automatically checked.

There are also leaks just from oversights. One of the massive oversights of many languages is allowing a Null Pointer. Now there's this mandatory check after every method returns. Do I actually have the thing the type told me or do I have null? People talk about the cost of Null Pointer exceptions in production. But what about the cost of adding an if statement after every method call? When we design an abstraction, we have to think hard about introducing corner cases and avoid them at all costs.

Rock on!