[jstimpfle]

If you need callbacks and generics, you're not writing performance code.

99% of code in the wild is comically inefficient and is doing the wrong thing, using way too generic data structures and algorithms for very concrete problems. C++ templates may be one way to make comically slow code faster by spending a lot of compile time. But it's often much quicker to just write straightforward concrete code that the compiler can easily optimize.

IMO C++ makes for slow programs for the sole fact that it compiles so slow (if you use its modern features), so you have much less time to actually iterate and improve.

[jmalicki]

If compilation is even more than 10% of the time it takes you to run your tests, you're probably not writing correct code. Compilation times don't even measure.

[jstimpfle]

So every time you compile, you run your test suite? I don't. And you trust that I have experience writing and compiling programs too...?

It should be a goal to keep rebuild times around 1 second (often not quite possible, but 3-5 seconds, even for full rebuilds, is often realistic). I edit, compile, run, edit, compile, run. Editing and running can often take as little as 1-3 seconds, and I sometimes do it dozens of times working in a row, working on a single improvement. That's why there is a 1 second rebuild time goal.

In practice I often work on codebases I don't fully control, but when the build times are excessively high, I will complain and try to improve. Build times longer than 10-15 seconds break the flow, they are a significant productivity hit. But they are quite common with C++ codebases (it can also be bad with C codebases by the way, but C++ is typically much worse because of templates and metaprogramming which is very slow).

> Compilation times don't even measure.

You must be joking. Do you even program?

[jmalicki]

You run your code before running tests? IMO that's bad practice.

1 second, seriously? Even the Linux kernel is based on C, and it doesn't even have compilation times approaching that.

I guess I also work on a lot of big data projects, where getting results will take... 48 hours or so, so anything shorter than that is basically some sort of unit test or dry run... so in that context, compilation times do not even register on the things slowing me down.

[jstimpfle]

Running the code immediately after making changes is the first line of testing. To run a huge test suite full of tests that are completely unrelated to the current changes would be stupid, it's a huge waste of time and energy.

Yes, seriously, have you ever written a project from scratch? A simple .c file with a thousand lines in it should easily build and start within 100ms. A compiler should be able to do basic parsing and codegen at 1M lines per core.

If your runs take 48h, of course you need a strategy to avoid noticing bugs only after dozens of hours running. You can't tell me that it is efficient to make changes and to wait for minutes or even hours before noticing that your code wasn't even syntactically valid, or maybe it did compile but your code had a small oversight and you need to start over building.

The Linux kernel is a HUGE project, one of the biggest around. Yes, a full rebuild takes a long time, depending on configuration. Incremental rebuilds do not, though.

I'm actually working on a Linux kernel module (distributed filesystem client), it's on the order of 40 KLOC. I can do a full rebuild in 10/15 seconds (debug/release), and that includes calling into the kernel's infrastructure and doing a lot of stuff that shouldn't have to be done. An incremental rebuild after changing a single .c file is about 3 seconds. Restarting the module (swapping for the newly built one) takes less than 10 seconds also. And this can be already a stressful bottleneck depending on the task. Say you're improving logging in a particular section of code, this can easily require 5-10 attempts.

I'm working on Desktop GUIs (2D/3D) too. You need a quick turnaround time as much as possible. Many changes are trivial but you want to do many small incremental improvements, recompile, run and test (manually), often with a breakpoint on the code you're currently working on.

The projects I'm working on are written in C or conservative C++, and most have from thousands to hundreds of thousands lines of code. They can be built from scratch in a short amount of time (< 10s for the smaller ones). And all of them do incremental builds in <= 10 seconds except when maybe changing the most central headers which essentially means a full rebuild.

You can also design a C/C++ codebase to always do a full rebuild, compiling everything as a single unit. That can be faster than trying to do incremental builds, for codebases of considerable size. Try out the popular raddebugger project, a complete build after checkout is about 3 seconds. It's ~300 KLOC I think.

[jmalicki]

Waiting 2 minutes for unit tests of the relevant module is not very long - using bazel helps to only run the relevant unit tests, not the full suite.

[jstimpfle]

It really depends on what you are doing. Sometimes I am not building in a day, just designing and thinking by editing. Sometimes I am refactoring for hours without building. But sometimes I am rebuilding every 10 seconds or so.