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by matheusmoreira 706 days ago
> CommonUtils.hpp

That's the root cause of the slow build. That file is likely to be depended on by way too many other files, triggering massive rebuilds when unrelated code is modified. The headers should be as granular as possible. Breaking up the generic utils file into many specific files will help contain the damage whenever any given file is changed.

I wish it was possible to track source code dependencies at the function level.
2 comments
OskarS 706 days ago
It's not just that. If ALL that was in the header was the function prototype, that adds basically nothing to the compile time. The problem is when you have significant codegen and parsing in headers, like you do with templates and class definitions and stuff like that.

Like, most C projects import enormous headers with gazillions of function prototypes without having a particularly measurable impact on compile times (compile times in C is quite good, in fact!)

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matheusmoreira 705 days ago
Right. For a second I forgot this was a C++ discussion.

Breaking up the headers into granular files should still help reduce the amount of instatiation that's going on at compile time provided there isn't much overlap in the headers included by the source files.

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erik_seaberg 706 days ago
GCC, LLVM, and MSVC++ all support precompiled headers. How often is a unique and minimal set of #includes worth the extra cost?
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matheusmoreira 706 days ago
That helps reduce the cost of parsing the headers but doesn't eliminate the issue. Changing a header triggers a rebuild of everything that includes it. If the header is ubiquitous, nearly everything gets rebuilt.

We want to reduce the set of rebuilt files to a minimum. That means separate headers so that files that use A don't need to be recompiled because B changed and A and B are defined in the same header.

Taking this logic to the extreme would lead to one file per type or function. I've read a lot of code that's structured this way and it works well. Editing lots of small files is a little annoying though. In the end it's a tradeoff.

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