[brundolf]

I would guess they're factoring this in:

> Turbopack is built on Turbo: an open-source, incremental memoization framework for Rust. Turbo can cache the result of any function in the program. When the program is run again, functions won't re-run unless their inputs have changed. This granular architecture enables your program to skip large amounts of work, at the level of the function.

Which would make that multiple an extremely rough estimate, highly-dependent on the situation. But it's still an exciting development

[IshKebab]

I wonder how they make that robust, given that Rust isn't pure and there's no way to force a function to be pure either.

[brundolf]

It's not very hard to stick to a pure-ish style even in languages that don't statically enforce it; JavaScript's MobX framework has the same constraint, as do React functions, and computed properties in Vue, etc. You don't really get any static help with functional purity in those cases, but thousands of programmers do it successfully every day

And while Rust doesn't strictly enforce purity, it does make it a lot easier to stick to in practice with its explicit `mut` keyword for local variables, references, and function arguments (including for the `self` argument on methods). There are various ways like RefCell to get around this if you're really trying to, but you have to go out of your way.