[Weebs]

This is a direction I've been pushing in partly because I'm using a significantly slower type inference algorithm in my language. I'm hoping with that and focusing on separate compilation I'll be able to keep the fancy inference without sacrificing the UX too much

[DanielHB]

When I used to program Java I absolutely loved hot code swap and was always amazed how little people even knew it was possible.

If you have a massive codebase no matter how fast your compiler is, re-compiling is going to be slow. But hot code swap is even better in that you can keep any state around without having to set it up all over again.

In Java I could change a method implementation with the program running and as long as I didn't touch my class state it would just work. Re-compilation was slow, but hot code swap was _fast_ and I maybe did a recompile 3-5 times per day total.

[mike_hearn]

Bear in mind that the underlying protocol used to request hot swap on Java is a lot more expressive than the standard HotSpot implementation is. If you use the Jetbrains Runtime (a fork of OpenJDK) or the GraalVM "Espresso" VM (a.k.a. Java on Truffle) then you can do way more hotswapping than you'd be able to normally.

Espresso goes further and doesn't only allow hot swapping but lets you write plugins that react to hot swaps of code:

https://www.graalvm.org/latest/reference-manual/java-on-truf...

If you use the Micronaut web framework then it will selectively re-initialize your app in response to hot swaps that need it. Pretty advanced stuff.

[DanielHB]

That is pretty neat, I haven't done serious Java development in ~10 years but I do vaguely remember hot swapping would eventually cause out of memory errors. I was using standard OpenJDK 6 and 7 at the time.