I found value in dissecting the different levels of change. For the sake of sanity though, we should do breaking changes. Breaking changes exist because we have limited capacity as individuals and an industry to maintain software. This is especially true for infrastructure that is supported by (limited) corporate sponsorship and volunteers. Breaking changes limit our window of focus to two or three snapshots of code, instead of having our window of focus grow without bound. Our limited capacity can still be effective as a library changes over time.
The most important point of this talk is here: "You cannot ignore [compatibility] and have something that is going to endure, and people are going to value" [0]. Breaking changes provide a benefit for library developers, but it is usually damage done to end users. As consumers we should weigh the cost of keeping up with breaking changes against the quality of a tool, and the extra capacity its developers are likely to have.
Agreed. Breaking changes can lead to alienation of user base, but I think there's a danger in lulling people into expecting that kind of constancy in software. It creates dependency of another kind. Maybe the trick is to vary features at some rate, getting users used to change and bringing them along.
In retail it used to be the case that you could go to the same store a month later and see the same shirt to buy. The Sears catalog [1] presented that sort of constancy for consumers. Today there's a lot of flux. Some of it actually engineered to prevent people from delaying purchasing decisions. In software we can and do introduce breaking changes for ease of maintenance, and that can be ok as long as people are used to it. It's making the choice to have a living ecosystem.
Additionally there are safer, usually reasonable, ways to deal with what would otherwise be breaking changes. Give the changed functionality a different name, create a new namespace/module without the removed functionality, or create a new library if you have introduced something fundamentally different (e.g., w.r.t. how you interact with it). That way your users can choose to refactor their code to use the change, rather than discover their expectations no longer match reality when they upgrade.
Who says you have to maintain old code? We're talking about simply not deleting it and establishing a discrete semantic for the new version as truthfully, a new version is new content which demands a new name to accurately and precisely describe it. If it didn't it would be like saying different content doesn't produce a different hash.
You're right, there is no obligation to maintain it. I think that misses the point though. The value in keeping the code is to allow the end user to continue to enjoy improvements in parts of the library that don't have breaking changes without upgrading those that do. You could continue to have security patches installed, for example. That value is much less when you don't do basic maintenance implement bug fixes and security patches.
Unless I'm missing something… the answer to that problem is to (a) factor the code sufficiently to then (b) create an abstraction (interface) that backs out the concrete implementation to the specifically desired version/functionality.
Hickey's other talk says hard is relative, and I happen to agree, especially when it comes to naming. The question is to what degree of exactness you can confirm what exists (in problems). That is a function of your degree of truthfulness. So it's "hard" only in the sense it's hard to approach 100% truthfulness. However, I have observed that one doesn't need 100%, one needs to be beyond a certain threshold of effective sufficiency. And according to human history, special, rare individuals are born who do exceed that threshold.
The most important point of this talk is here: "You cannot ignore [compatibility] and have something that is going to endure, and people are going to value" [0]. Breaking changes provide a benefit for library developers, but it is usually damage done to end users. As consumers we should weigh the cost of keeping up with breaking changes against the quality of a tool, and the extra capacity its developers are likely to have.
[0] https://youtu.be/oyLBGkS5ICk?t=4177