Comment by Jach

I don't think it's fair to dismiss criticism because of skill. I said I think it's a bad book, and my most disliked, but it's not worthless, and if it's all someone has, they can indeed learn things from it even if they won't learn very much per page. However, there are many other books available, and by my own opinion all of them that I've read are superior. Any value you'd get from APOSD, you'd get from any book aimed at or inclusive of a similar audience, and the other book would give even more value that's absent from APOSD. (As another example, I was introduced to The Pragmatic Programmer in college. I believe it can serve the role of APOSD just fine but I never liked it enough to finish it, so perhaps I'd rank it lower if I did.) I also think you'd get most of the value just by writing more programs.

Anyway, the favored book I did highlight, The Practice of Programming, shares some things with APOSD: it's also not academic, is also quite short (maybe 70 pages longer), and is also more productively read earlier in one's career or study but it's still appreciable by those with more experience. You'll learn things about design. But it has so much more than APOSD: you'll learn things about implementation and debugging and considerations for libraries for yourself or others rather than just applications, and so much more in so few pages; just lots of things central to writing programs, which is the fundamental task at the end of the day, more so than just "designing" things.

I guess another complaint is that APOSD just doesn't have enough code in it. And perhaps an implicit philosophy I have is that you can't actually master good design without writing good code. Learning from the feet of masters is a good way to learn, but they actually have to teach by example. To that end, The Practice of Programming has many programs as examples (like a markov chain text generator, written in multiple languages with performance and effort-of-writing comparisons) and invites the reader to do many various exercises (like commenting on comments, or rewriting part of an example to use a different implementation decision and compare the different approaches).

When that book happens to make a claim I agree with, I don't tend to also just dismiss it as a platitude, because it's better argued and reasoned (or argued and reasoned at all), and supported and contains even more information to consider. Let's expand the bit I quoted about interfaces from APOSD, it's actually from the section on exceptions.

"Defining away exceptions, or masking them inside a module, only makes sense if the exception information isn't needed outside the module. ... However, it is possible to take this idea too far. In a module for network communi­cation, a student team masked all network exceptions: if a network error occurred, the module caught it, discarded it, and continued as if there were no problem. This meant that applications using the module had no way to find out if messages were lost or a peer server failed; without this information, it was impossible to build robust applica­tions. In this case, it is essential for the module to expose the exceptions, even though they add complexity to the module's interface. With exceptions, as with many other areas in software design, you must determine what is important and what is not important. Things that are not important should be hidden, and the more of them the better. But when something is important, it must be exposed (Chapter 21 will discuss this topic in more detail)."

I find the student example here pretty weak, but it'd be stronger if the actual code was shown and developed, especially if done in a context where it's understandable how the students might have thought it was a good idea at first, rather than just making an obvious mistake because they're students. Chapter 21 does discuss things in more detail, but not much more, and again there are no code examples much beyond pointing back to a prior chapter's dozen lines of strawman Java. It starts off with:

"One of the most important elements of good software design is separating what matters from what doesn't matter. Structure software systems around the things that matter. For the things that don't matter as much, try to minimize their impact on the rest of the system. Things that matter should be emphasized and made more obvious; things that don't matter should be hidden as much as possible."

Does that not read to you as terribly verbose and information sparse? Capable of eliciting a "duuuuuh" even from a beginner programmer? Almost tautological even? The rest of the chapter is similar and doesn't actually give much more information at all. Sure there are a few tidbits of use in there, like the idea of "leverage" and what that means as an approach, and a throw-away line that deserved more elaboration about shallow classes needlessly increasing what seems "important". (Yegge's "Execution in the Kingdom of Nouns" post is a good expansion of that and other things, if it's at all helpful to understand examples of what I find valuable in comparison to this book.)

Let's compare now some similar bits from The Practice of Programming. This comes as a partial summary after a worked section on designing an interface for parsing CSV files in C and C++ with many design decisions detailed and discussed.

"Good interfaces follow a set of principles. These are not independent or even consistent, but they help us describe what happens across the boundary between two pieces of software. *Hide implementation details.* The implementation behind the interface should be hidden from the rest of the program so it can be changed without affecting or breaking anything. There are several terms for this kind of organizing principle; information hiding, encapsulation, abstraction, modularization, and the like all refer to related ideas. An interface should hide details of the implementation that are irrelevant to the client (user) of the interface. Details that are invisible can be changed without affecting the client, perhaps to extend the interface, make it more efficient, or even replace its implementation altogether. The basic libraries of most programming languages provide familiar examples, though not always especially well-designed ones. The C standard I/O library is among the best known: a couple of dozen functions that open, close, read, write, and otherwise manipulate files. The implementation of file I/O is hidden behind a data type FILE*, whose properties one might be able to see (because they are often spelled out in <stdio.h>) but should not exploit."

If you squint, kind of says much the same thing, right? But it's richer, includes whys, and points to a real-life example, not a student project. It also criticizes the C I/O library right after because of its exposure of publicly visible data.

More on the topic of exceptions, the book takes a rather classic approach that I don't fully endorse ("Use exceptions only for exceptional situations"), but one unique bit is a more thorough treatment of handling errors without having to alter control flow, and why that might be important. In the markov generator program, one worry is that there might not be enough input to start the algorithm. One could exit prematurely (with a special value or an exception) but the book chooses instead to do some padding to ensure the problem goes away. Emphasis mine:

"Adding a few NONWORDs to the ends of the data simplifies the main processing loops of the program significantly; it is an example of the technique of adding sentinel values to mark boundaries. As a rule, try to handle irregularities and exceptions and special cases in data. Code is harder to get right so the control flow should be as simple and regular as possible."

You don't have to take this rule as given, you immediately see it in action, and an exercise later invites you to re-implement without a sentinel value to compare.

APOSD has an entire chapter on errors, but this idea is only barely hinted at in the whole chapter on errors with the idea of defining errors out of existence (it uses a more controversial example, I think, from TCL) and this bit that clarifies that by "exception" he doesn't necessarily mean a stack-unwinding thing: "However, exceptions can occur even without using a formal exception reporting mechanism, such as when a method returns a special value indicating that it didn't complete its normal behavior. All of these forms of exceptions contribute to complexity."

It's just such a shallow treatment, and I think that last bit is more focused on the other basic idea that Practice of Programming spells out:

"Exceptions should not be used for handling expected return values. Reading from a file will eventually produce an end of file; this should be handled with a return value, not by an exception."

That's followed by a code example showcasing said behavior that doubles as a less-strawman swipe at classical Java. (The Java code loops in.read() until it's -1, and has separate exception handlers for a file not found exception, which the book thinks isn't all that exceptional, and a generic IOException.) But to APOSD, it doesn't seem to matter, they all just contribute to complexity. Maybe they contribute to different degrees? (This would require an objective definition of complexity that lets you count the twists, though.) Maybe leveraging the type system (if you have such a language) to define away errors should be mentioned? Maybe (though this one is truly a rhetorical fever dream wish) acknowledgement of Common Lisp's condition system as yet another powerful alternative should be given?