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Comment by mikepurvis | Hacker News Reader

From an overall performance point of view, I wonder how the timing works out for the compiler to run your unit tests like this vs to produce and invoke a binary.

I bet it's mostly a wash, and the ergonomics of conventional gtest macros look way better to my eye.

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The idea to let the compiler run the tests only works if you constexpr everything, which means putting all code in headers. This effectively means giving up on separate compilation. Worse, if you use some mixture (most code in headers but you still have >1 compilation unit), your compile times completely explode as essentially all code is compiled repeatedly for each unit.

There are other ways to do this. I made a proof of concept of using linker sections to allow you to sprinkle tests within the implementation inline once... https://github.com/cozzyd/examc (this is obviously not production-ready, just serves as a proof of concept).

Basically the idea is that the test code gets written to a different linker section that your test runner can iterate through, when tests are enabled. This is easy on gcc because it generates automatic constants for the beginning and end of different linker sections. There may be away to do this with clang as well, but I never use clang.

Pragmatically you can write your code in such a way that you can get immediate feedback in your IDE as you write the code if a static assert fails as you are implementing your function.

You could of course set up your runtime tests in a similar way, having the ide run them back to back as you are writing code, but it is more complicated, especially if the code is in an intermediate state that it is not fully compilable.

So in the end it is not a huge breakthrough, but having compile time tests is still quite a nice feature.

Hmm, there are obvisouly trade offs (it depends on the compiler how many tests, how are they written, etc.) but for apples to apples comparision the gtest binary would have to be either compiled with sanitizers (that would be probably slower to compile than static_assert tests without sanitizers) or run with valgrind or similar (execution would be much slower, static_asserts tets don't have to be executed, compiles=green).

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