> C interop is simple and elegant
C interop in go is super slow: https://github.com/dyu/ffi-overhead
C interop in go is super slow: https://github.com/dyu/ffi-overhead
So calling C from Go for small functions isn't a performance gain. You should write those in Go. The calling of C is great for linking against larger libraries, which cannot be ported to Go. And for that it works nicely and is fast enough.
It may be fast enough for you, but it certainly isn't for many other people. golang will for example never grow a large mathy/scientific ecosystem, because of it.
I find I use Go quite often to build relatively compact tools and services that need to use some features of a fully-featured and popular C library to perform some complex function that would be expensive and time-consuming to implement.
A recent example of this is using `libusb` and `libgphoto2` to enumerate DSLR cameras attached over USB and capture images from them in response to some other events, with a small web UI on top. It's maybe a few dozen lines of Go to call some enumeration and capture functions, and then I get a nice byte slice with all the data I want. There is minimal friction, the interaction is clear, and any performance cost is worth paying because of the simplicity of the interaction.
It's entirely true, and a well-known caveat, that the C FFI is slow. This makes it inappropriate for some use-cases, but entirely suitable for others.