[rpep]

> Most FFI boundaries incur their own performance cost. I’m not sure about Python, but I wouldn’t be surprised if FFI to rust in a hot loop is often slower than just writing the same code in Python directly. And it’s not always easy to refactor to avoid this.

They definitely do, but I’d usually suggest that if you find this an issue then perhaps the function you’re exposing from the compiled language should be higher level, with more work done in the compiled code to avoid the overhead of returning control back to the interpreted language.

[josephg]

Maybe. But that can also be a self tightening knot. Sometimes there’s no elegant place to cleave a program or library in two, and you really just want to pick a single language for the whole project.

Mixing languages can also be a bit of a disaster for maintainability. Refactoring codebases which meaningfully span multiple languages is miserable work.