alt Hacker NewsBecause Russt and Swift are doing much more work than a C compiler would? The analysis necessary for the borrow checker is not free, likewise with a lot of other compile-time checks in both languages. C can be fast because it effectively does no compile-time checking of things beyond basic syntax so you can call foo(char) with foo(int) and other unholy things.
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These languages do more at compile time, yes. However, I learned from Ryan's discord server that he did a unity build in a C++ codebase and got similar results (just a few seconds slower than the C code). Also, you could see in the article that most of the time was being spent in LLVM and linking. With a unity build, you nearly cut out link step entirely. Rust and Swift do some sophisticated things (hinley-milner, generics, etc.) but I have my doubts that those things cause the most slowdown.
That’s not a good example. Foo(int) is analyzed by compiler and a type conversion is inserted. The language spec might be bad, but this isn’t letting the compiler cut corners.
If you'd like the rust compiler to operate quickly:
* Make no nested types - these slow compiler time a lot
* Include no crates, or ones that emphasize compiler speed
C is still v. fast though. That's why I love it (and Rust).
This explanation gets repeated over and over again in discussions about the speed of the Rust compiler, but apart from rare pathological cases, the majority of time in a release build is not spent doing compile-time checks, but in LLVM. Rust has zero-cost abstractions, but the zero-cost refers to runtime, sadly there's a lot of junk generated at compile-time that LLVM has to work to remove. Which is does, very well, but at cost of slower compilation.
The borrow checker is usually a blip on the overall graph of compilation time.
The overall principle is sound though: it's true that doing some work is more than doing no work. But the borrow checker and other safety checks are not the root of compile time performance in Rust.