Trailing Commas

[Johannes Spangenberg]

Thanks for the responses.

> I don't really expect this feature to happen, but I feel like this 
> thread ought to include some mention of the actual benefits of the 
> feature?

You are absolutely right. Thanks for listing them. The Scala project 
also listed advantages and drawbacks in SIP-27 - Trailing Commas 
<https://docs.scala-lang.org/sips/trailing-commas.html> before its 
implementation.

> For every person who has a strong preference in favour of allowing 
> trailing commas where they’re not allowed today you’ll find another 
> with an equally strong preference against allowing them. Additionally, 
> if this option exists, people will want to write or update style 
> guides preferring one style or the other. So the result is a lot of 
> time, and possibly completely disproportionate emotion, spent for 
> what, at best, is little gain. To me this sounds like the kind of 
> change that is bound to require more effort — not on the 
> implementation perhaps, but in debate — than it’s worth.

If I understand correctly, you're pointing out the effort required to 
determine if the entire community would support this change? That is a 
fair point. I still want to mention that in my personal experience 
outside the Java ecosystem, discussions around trailing commas haven't 
been as contentious as those involving whitespaces, tabs, or line 
breaks. They've generally leaned towards supporting trailing commas. 
This is why I unfortunately failed to list the advantages as I did not 
consider trailing commas particularly controversial by themself. This 
might be a personal bias of course. Nevertheless, I acknowledge that 
there might be more pressing topics at the moment.

>  - every change we made that "makes life easier for code generators" 
> makes life harder for parsers, and it is not clear that privileging 
> one over the other is a good idea;

I think the main drawback lies in the requirement to change existing 
tooling. However, tools have to adapt to new Java versions all the time. 
Adding support for trailing commas to a parser, in my experience, 
requires minimal changes and doesn't significantly complicate the 
implementation. When I added support for trailing commas to my parser of 
the Nix Expression Language, I only had to make a small change to a 
single line (besides adding tests).

> Your point about smaller diffs and reordering lists is correct, and 
> (I'm guessing) what originally motivated this feature.

Yes, you are right. It's all about making it easier to work with lists.

> However, that motivation only applies when the items you are listing 
> are normally or typically placed on separate lines.

I think putting method arguments onto separate lines is also somewhat 
common, especially when considering varargs. I also imagine it quite 
useful for the component list in records. For the remaining language 
constructs, it might be less common, but I have definitely seen cases 
where other constructs were placed on separate lines as well.

Thanks again. I will take from this conversation that trailing commas 
are unlikely to be prioritized anywhere soon.

Best regards,
Johannes
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.org/pipermail/amber-dev/attachments/20231201/e6aa20cb/attachment.htm>