Most filters in `alloc` should be possible to implement without alloc

[Kijewski]

PR #466 can serve as a great example on how to convert filters to not use alloc.

I think it's possible for

• linebreaks | linebreaksbr | paragraphbreaks (Filters linebreaks, paragraphbreaks and linebreaksbr only need core #486)
• upper | uppercase
• wordcount (Make wordcount filter work with core only #480)

I think it would be possible for ↓, but Greek's sigma-rules would make it comparatively more difficult than other other filters:

• capitalize
• lower | lowercase
• title | titlecase

I don't think it would be possible for trim, because there can be an unrestricted amount of whitespaces in between other characters.

• trim

I don't think it's possible for ↓, because format! simply needs alloc:

• fmt
• format

[GuillaumeGomez]

One big question I have is: what about performance. Just taking a look at upper, the to_uppercase source code is quite optimized and definitely not easy to get right. Also, having an allocation is likely faster than multiple write calls (except if it is inside a buffer like a String), no?

[Kijewski]

Yeah, we definitely have to measure if such a change makes the code slower. If someone directly writes to the PTY, a TCP stream, a file, smth., then they deserve all the pain they get, IMHO. :) BufWriter exists for a reason.

Also, unrelated, do you know if are there plans to make the {core,alloc,std} source code clickable? I love that feature to get a quick overview how the code is connected.

[GuillaumeGomez]

I'd love to but it's out of my hands. Please open an issue on the rust repository to try to get support to make it happen. :)