Comment by ajuc

A lot depends on what your language and its ecosystem can support. For instance, the kind of monadic stuff people do with Haskell and Scala can compress programs tremendously, but then I've worked in a codebase that tried the same things in C++ - and there, the line count expands, because the language just can't express some of the necessary concepts in a concise way.

I coded this way for a while and found it makes the code easier to read and easier to reason about. Instead of your function being

  func foo() {
    // do A.1
    // do A.2
    // do B.1
    // do B.2
    // etc...
  }

It becomes

  func foo() {
    // do A
    // do B
    // etc...
    // func A()...
    // func B()...
  }

When the func is doing something fairly complicated the savings can really add up. It also makes expressing some concurrency patterns easier (parallel, series etc...), I used to do this a lot back in the async.js days. The main downside seems to be less elegant automated testing from all the internal state.

No; I wouldn't do it if I was just calling them once each in a particular order. And I don't often use this trick for simple functions. But sometimes long functions have repeated behaviour.

For example, in this case I needed to do two recursive tree walks inside this function, so each walk was expressed as an inner function which recursively called itself, and each is called once from the top level method:

https://github.com/ottypes/json1/blob/05ef789cc697888802e786...

I don't do it like this often though. The code in this file is easily the most complex code I've written in nearly 3 decades of programming. Here my ability to read and edit the code is easily the most important factor. I think this form makes the core algorithm more clear than any other way I could factor this code. I considered smearing this internal logic out over several top level methods, but I doubt that would be any easier to read.

A recommended reading https://www.amazon.com/Refactoring-Improving-Existing-Addiso...