Essence of Software

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1. DarmaniDec 2024
   TCP is great. Long chains of one-line functions that just permute the arguments really suck. These both get called abstraction, and yet they're quite different.

   But then you hear people describe abstraction ahem abstractly. "Abstraction lets you think at a higher level," "abstraction hides implementation detail," and it's clear that neither of those things are really abstractions.

   As the OP mentions, we have a great term for those long chains of one-line functions: indirection. But what is TCP? TCP is a protocol. It is not just giving a higher-level way to think about the levels underneath it in the 7-layer networking model. It is not just something that hides the implementations of the IP or Ethernet protocols. It is its own implementation of a new thing. TCP has its own interface and its own promises made to consumers. It is implemented using lower-level protocols, yes, but it adds something that was fundamentally not there before.

   I think things like TCP, the idea of a file, and the idea of a thread are best put into another category. They are not simply higher level lenses to the network, the hard drive, or the preemptive interrupt feature of a processor. They are concepts, as described in Daniel Jackson's book "The Essence of Software," by far the best software design book I've read.

   There is something else that does match the way people talk about abstraction. When you say "This function changes this library from the uninitialized state to the initialized state," you have collapsed the exponentially-large number of settings of bits it could actually be in down to two abstract states, "uninitialized" and "initialized," while claiming that this simpler description provides a useful model for describing the behavior of that and other functions. That's the thing that fulfills Dijkstra's famous edict about abstraction, that it "create[s] a new semantic level in which one can be absolutely precise." And it's not part of the code itself, but rather a tool that can be used to describe code.

   It takes a lot more to explain true abstraction, but I've already written this up (cf.: https://news.ycombinator.com/item?id=30840873 ). And I encourage anyone who still wants to understand abstraction more deeply to go to the primary sources and try to understand abstract interpretation in program analysis or abstraction refinement in formal verification and program derivation.

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2. tedyoungDec 2021
   Haven't finished reading it yet, but it's been enlightening and thought-provoking: "The Essence of Software" by Daniel Jackson.
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