“Before” (not “Beyond”) Design Patterns

(N.b.: This has been languishing at the bottom of my blog heap for years; time to get it into the sun.)

The 2013 article Beyond Design Patterns takes the approach of reducing all design patterns to a single pattern: “Abstracting Communication Between ‘Components’.” The author concludes, in part:

Instead of focusing on design patterns, I would suggest focusing on understanding how communication between objects and components happens. How does an object “decide” what to do? How does it communicate that intention to other objects.

Are design patterns useful? Absolutely. But I’ll assert that once you understand OOP and object communication, the patterns will “fall out” of the code you write. They come from writing OOP.

This strikes me as misapplied reduction. Sure, it’s true that, at a lower level or scope, it might be fair to say that “the pattern is ‘communication.’” But it is also true that, at a somewhat higher level or scope, communication between “which things” in “what way” is also fair. So the article might better be titled not “Beyond Design Patterns” but “Beneath Design Patterns” or “Before Design Patterns”. The concepts illustrated are not consequences of or improvements on design patterns; they are priors to design patterns.

The analogy that came to my mind was one of molecules and atoms. An imaginary article on chemistry titled “Beyond Molecules” might thus conclude …

Instead of focusing on molecules, I would suggest focusing on understanding how interaction between atoms happens. How does an atom “decide” what to do? How does it communicate that intention to other atoms?

Are molecules useful? Absolutely. But I’ll assert that once you understand atoms and atomic interaction, the molecules will “fall out” of the formulas you write.

… which is true enough for as far as it goes, but it is also revealed as a rather superficial and mundane observation when presented this way. Atoms are not “beyond” molecules.

So: molecules are a proper unit of understanding at their level or scope. Likewise, design patterns are a proper unit of understanding at their own level. Reducing them further does not show you anything “beyond” – it only shows you “because.”

A “Systems” Addendum To Semantic Versioning

tl;dr: When using semantic versioning, consider not only changes to the public API, but also changes to system requirements.


Semantic Versioning concentrates on the public API signature as the determiner of when to change version numbers. If the public API changes in a backwards-incompatible way, then you have bump the major version number. When I upgrade a dependency to a minor or patch version, I am hypothetically assured that the upgrade will be successfully completed, and that I will not have to change anything about my existing system or codebase.

However, I have come to think that while SemVer’s concentration on the public API is a necessary indicator of the upgradability without other changes, it is not a sufficient indicator. Here’s a real-world upgrade scenario:

  1. Package 1.0.0 is released, dependent on features available in Language 4.0.0.

  2. Package 1.1.0 is released, with a public API identical to 1.0.0, but is now dependent on new features available only in Language 4.1.0.

SemVer is honored here by both the Package and the Langauge. Neither has introduced backwards-incompatible public API changes: the Package API is unchanged, and the Language API adds new backwards-compatible features.

But now the Package internals depend on the new features of the Language. As such, it is not possible for the Package 1.0.0 consumers to upgrade to Package 1.1.0 without also upgrading to Language 4.1.0. If they try to upgrade, the system will break, even though SemVer indicates it should be safe to upgrade.

It looks like there is more to backwards compatibility than just the public API.

II.

Some will argue that when the package requirements are properly specified in a package manifest, the package manager prevent a break from occurring in the above scenario. The package manager, reading the manifest, will note that Language 4.1.0 is not installed, and refuse to upgrade Package from 1.0.0 to 1.1.0.

However, this is beside the point that I am trying to make. Yes, the package manager prevents breaking installations based on a manifest. But that prevention does not mean that the changes introduced in Package 1.1.0 are backwards-compatible with a system running 1.0.0. The 1.1.0 changes require a system modification because of a requirements incompatibility.

So it is true that the package manager provides a defense against breaks, but is also true that the version number of the package does not indicate there is a backwards incompatibility with the existing system. It is the indication of incompatibility (among other things) that makes SemVer valuable.

III.

I opine that requiring a change in the public environment into which a package is installed is just as major an incompatibility as introducing a breaking change to the public API of the package. To cover that case, I offer the following as a draft addendum to the SemVer spec:

  • If the package consumer has to change a publicly-available system resource to upgrade a package, then the package upgrade is not backwards-compatible with the existing system, and the package SHOULD receive a major version bump.

Using “SHOULD” makes this rule somewhat less strict than the MUST of a major version bump when changing the package API. It’s possible that Language 4.0.0 is no longer supported or installed on any of the target systems, in which case it might be reasonable that a Package minor version could require a change to the Language version. But you do need to have a good technical or practical reason (not a marketing reason 😉 to avoid the major version bump when changing the public system requirements for the package.

(You may also wish to review Romantic Versioning for an additional take on Semantic Versioning.)

Hacking, Refactoring, Rewriting, and Technical Debt

(Not so much “lessons” here, as “observations and recollections.”)

I.

From ESR, How To Learn Hacking:

  • Hacking is done on open source. Today, hacking skills are the individual micro-level of what is called “open source development” at the social macro-level. [2] A programmer working in the hacking style expects and readily uses peer review of source code by others to supplement and amplify his or her individual ability.
  • Hacking is lightweight and exploratory. Rigid procedures and elaborate a-priori specifications have no place in hacking; instead, the tendency is try-it-and-find-out with a rapid release tempo.
  • Hacking places a high value on modularity and reuse. In the hacking style, you try hard never to write a piece of code that can only be used once. You bias towards making general tools or libraries that can be specialized into what you want by freezing some arguments/variables or supplying a context.
  • Hacking favors scrap-and-rebuild over patch-and-extend. An essential part of hacking is ruthlessly throwing away code that has become overcomplicated or crufty, no matter how much time you have invested in it.

This strikes me as the opposite of, or at best orthogonal to, the practice of refactoring a large and long-existing codebase, especially that last. “Scrap and rebuild” is essentially “rewrite from scratch” and that is almost always a losing proposition in terms of time and budget.

But then, the description also says hacking is “lightweight, exploratory, modular” — so perhaps it is possible to hack at components within a larger or critical system, and then refactor the system using that result. Cf. Hacking and Refactoring, also from ESR.

II.

I used to work for a consulting company with One Big Client (and a few smaller ones). This One Big Client generated a staggering amount of money; its business model was such that even a few minutes of downtime would result in large losses (technically “lost revenue” but the effect is the same).

The consultancy’s director of development for the One Big Company didn’t “believe” in technical debt. Or rather, he thought technical debt was a non-issue. He would write, or demand writing, some of the most horrific code, as long as it was written *quickly*, because the time constraints for the One Big Client were so overwhelming. There was no refactoring; he and his team would iterate fast, then wipe out the entire codebase and start all over again on a regular basis. (By “regular” I mean every 3-6 months). Any technical debt that was incurred was tiny in comparison to the monetary returns — although it did take a toll on the programmers themselves.

Given ESR above, that’s clearly a “hacking” approach to a critical codebase. Also, it’s clear that *sometimes* a full-on rewrite might be the right thing to do, provided the right context. But I’m betting the vast majority of developers (I’m talking “five nines” here) are not operating in the context of that One Big Client and that particular consultancy. These were “skilled developers knowingly writing low-quality code” — not to be confused with “*un*skilled developers *un*knowingly writing low-quality code.” (Cf. Mehdi Khalili: “On Bad Code.”)