The mental model for when a trailing comma is allowed may be clear to a language designer, compiler engineer, or from a parser perspective, but as a developer who uses the Swift language and has been writing Swift every day for the last 10 years I find the rules and exceptions to be pretty confusing.

https://forums.swift.org/t/se-0439-allow-trailing-comma-in-comma-separated-lists/72876/25 このコメントには同意だな。普段からコンパイラやParserを書いたりしてる人と一般のユーザーとは違うはずだ、っていう。

SE-0439: Allow trailing comma in comma-separated lists

I follow along with many Swift Evolution proposals and am rather active in the community and don't comment very often, but I felt rather compelled to chime in on this with a different perspective. What is your evaluation of the proposal? A pretty strong -1. I'd like to take a few examples from the proposal itself of what wouldn't be allowed ...