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Comment by piinbinary | Hacker News Reader

I just downloaded and built that. I was presently surprised to find that it "just worked." It picked up my .emacs, my color theme, my extensions and all the associated data. The only observable difference between it and real emacs was that it ran significantly slower. Presumably that will go away with time.

Great work!

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I'm surprised there would be a significant speed difference. My understanding is that they're mostly rewriting the C parts in Rust, which shouldn't change the speed much. Maybe byte-compilation is disabled for remacs or something? Or perhaps some debug options are enabled by default?

Byte-compilation isn't disabled. The slowness is due to a couple things. First is the bindgen layer between Rust and C slowing down certain calls. Porting so far has been wide rather than deep, so Rust code ends up having to call C sooner rather than later. In addition most of the ported functions have been rewritten in a pretty naive style that doesn't take full advantage of Rust. There was some discussion in Gitter or issues about this a couple weeks back, but I cannot seem to find it tonight. Apologies.

This is something I've been wondering about. Porting from C to Rust one function at a time sounds nice, but presumably the end result would be a Rust program with an identical program structure to the original C, which as a result doesn't take very much advantage of Rust's features. Is the goal to port all the way to Rust and then refactor to actually make the code Rust-ish?

Yep! Even now it's not quite as bad as identical program structure. I mean, the high-level is fairly similar, but even now individual functions can look significantly different.

Emacs' C is already largely written in a high-level, macro-rich style to deal with Lisp objects (tagged pointers). So Rust already gives wins there w.r.t. more explicit types and From/Into impls over macros.

And over the last couple weeks there has been discussion about replacing xml.c with a native Rust backend for XML parsing.

Is it release build or debug build?

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