| There's a lot here, just a few comments: > Although GSG does not forbid them categoricaly, it says to “Avoid using forward declarations where possible”. However forward declarations are useful in contexts like the following [...] Yes, circular data structures are a great reason to use a forward declaration; probably the best one. I think it is a perfect example of why the recommendation against forward declarations is not a prohibition. Please, please do not forward-declare types you do not own. It constraints the way those types can be refactored. More info here: https://abseil.io/about/compatibility#what-users-must-and-mu... > The rule basically says that global/static variables with non-trivial constructors and destructors are not allowed. While it’s true that initialization/destruction order of globals between translation units is not defined and can pose problems, this rule is overly prohibitve. Globals like this are not problematic and very useful: A safe alternative to this is to use a static object inside a function. This can serve the same purpose without the gotchas. > Even the inter-translation unit ordering is not a huge problem – Stroustrup discusses it in his D&E book. Experience says otherwise. In the protobuf code-base we have to put a thread-safe initialization check in all of our constructors because we have to statically initialize our default instances, but we can't guarantee these static initializers will run before other static initializers that use them. Static initialization ordering is a real and difficult problem. |