CppCon 2017: Titus Winters “C++ as a "Live at Head" Language”

There is a great talk by their C++ dev team about how a build everything from source, mono repo really helps with C++ change enablement [VIDEO] Personally, I’d have to agree that at a minimum a mono repo per distinct product role (server side in one mono repo, desktop software in one mono repo) is immensely valuable.

Relevant talk by Google at CppCon last year focused on C++, but really talks about getting rid of versioning in general. [VIDEO]

> You are totally correct that to achieve the same performance, correctness, and overall master level "green"ness in a multirepo system you would have to either define or detect dependencies and dependent repos, build the entire affected chain, and test the result. That part is much easier in monorepo. You also would need to do that as an atomic operation (in the mono-repo + especially with a commit queue you're building on the atomicity of git). Having to unwinding that transaction if you aren't atomic can get you into a big mess at larger scales. Here's a good related talk: C++ as a "Live at Head" language: [VIDEO] by Titus Winters (from Google).

Semantic versioning isn't a silver bullet, unfortunately, due to the 'Diamond Dependency Problem'. That is, A depends on B and C, but B and C depend on different versions of D. Easy to fix, until you scale that up to thousands of nodes in a dependency graph. This talk is one of the better ones about this: [VIDEO]

For another perspective on “semver is a lie,” see the “Live at Head” talk from Titus Winters of the Google core C++ team. [VIDEO] TL;DW: By Hyrum’s law, at sufficient scale, there’s no such thing as a non-breaking change (including changing comments). Embrace that, and test sufficiently that you can always take the latest dependency but detect when it breaks.

> If you go listen to Google people talk about dependency/version management. It's like they think it's global lock vs inconsistency. Monorepo or chaos. This false choice irks me. I watched this talk: [VIDEO] I’d say this is a much more nuanced look at dependencies & versioning. We all know these days that something like semantic versioning is not enough, because it is too easy to depend on behavior which the developers of your dependencies did not expect you to depend on. So you need something more powerful than just having a bunch of developers get together and agree not to break each others’ code. Bazel is a part of that solution—if you can analyze and understand the dependencies in a project, and do so in a very automatic and reliable way, you can provide people with tools tools for updating downstream code when upstream code changes. I think people are focusing too much on Bazel as only a build system and not as part of a platform for building developer tooling, and people are focusing too much on Bazel’s original incarnation as a build system for a massive monorepo. I think there’s also a reality that we must deal with that is—as software gets larger and more complex, and as we have more dependencies, relying on version pinning for stability is losing ground as a technique for making our software more reliable. We have many more dependencies in our software now, so just subscribing to a mail feed of all of the version bumps in the libraries you use would be enough to dr

Usually that problem is dealt with combination of: * Automation. * Ability to change other people's code safely, possibly gated by code review approval. Cultural and technical (e.g. unit tests must exist and be maintained) barriers may apply. * Making incremental changes that are backward compatible (at least until you migrated all clients so you can cleanup later) I recommend this talk [VIDEO] (even if the scope is broader than your question) (ex-googler)

Lots of posts here frame it like "Yes, it's a bit of a complex language, but the C++ committee has the difficult job of keeping everything backwards compatible, so it's understandable." But that's not the reality. The reality is that they (or Stroustroup) made that decision, and that decision was a mistake. The correct way to deal with backwards compatibility issues is the way Go does it, namely to write tools to automatically upgrade code to a newer API [1]. And as that smug Google guy explained here [2], they have something like this for C++, too. They just don't bother sharing it with us peasants. The fundamental mistake of C++ is to religiously keep backwards-compatibility with everything for all eternity. It's so easy to say that backwards-compatibility is a good thing. It's obvious! But ultimately that decision is the reason for all the problems that C++ has. [1] [LINK] [2] [VIDEO]