[marcusbuffett]

I strongly recommend "A Philosophy of Software Design". It basically boils down to measuring the quality of an abstraction by the ratio of the complexity it contains vs the complexity of the interface. Or at least, that's the rule of thumb I came away with, and it's incredible how far that heuristic takes you. I'm constantly thinking about my software design in these terms now, and it's hugely helpful.

I didn't feel like my code became better or easier to maintain, after reading other programming advice books, including "Clean Code".

A distant second recommendation is Programming Pearls, which had some gems in it.

[narnarpapadaddy]

Implicitly, IIRC, the optimal ratio is 5-20:1. Your interface must cover 5-20 cases for it have value. Any fewer, the additional abstraction is unneeded complexity. Any more, and your abstraction is likely too broad to be useful/understandable. The example he gives specifically was considering the number of subclasses in a hierarchy.

It’s like a secret unlock code for domain modeling. Or deciding how long functions should be (5-20 lines, with exceptions).

I agree, hugely usual principle.

[abhis3798]

This is a good rule of thumb, but what would be a good response to have interfaces because, "what if a new scenario comes up in the future"?

[kragen]

Maybe some examples would clarify your intent, because all the candidate interpretations I can think of are absurd.

The sin() function in the C standard library covers 2⁶⁴ cases, because it takes one argument which is, on most platforms, 64 bits. Are you suggesting that it should be separated into 2⁶⁰ separate functions?

If you're saying you should pass in boolean and enum parameters to tell a subroutine or class which of your 5–20 use cases the caller needs? I couldn't disagree more. Make them separate subroutines or classes.

If you have 5–20 lines of code in a subroutine, but no conditionals or possibly-zero-iteration loops, those lines of code are all the same case. The subroutine doesn't run some of them in some cases and others in other cases.