Bug #19918: Should `a[&b]=c` be syntax valid?

• Status: Closed
• Assignee: yui-knk (Kaneko Yuichiro)
• Target version: -
• ruby -v: ruby 3.3.0dev (2023-10-11T04:46:58Z master 40ab7b8c24) [x86_64-linux]
• Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN

[tompng (tomoya ishida)]

These codes are syntax valid now. Prism parses it as syntax error.

a[&b]=c
a[&b]+=c
a[&b]&&=c
a[&b]||=c

Is this syntax intentional or should be error?

Issue of Prism
https://github.com/ruby/prism/issues/1636

It's added in test_parse.rb
https://github.com/ruby/ruby/blob/40ab7b8c244de20007cb45846f41de3a01f7ea0c/test/ruby/test_parse.rb#L502

[mame (Yusuke Endoh)]

Assuming this is intentionally valid, I wonder if a[&b] = c should evaluate b before c.

[baweaver (Brandon Weaver)]

Is it bad that my first consideration is how this might be abused to do bad things for code golfing reasons? I blame mame.

[Eregon (Benoit Daloze)]

mame (Yusuke Endoh) wrote in #note-1:

Assuming this is intentionally valid, I wonder if a[&b] = c should evaluate b before c.

That's the kind of complications which I think illustrates the Ruby syntax shouldn't support such edge cases.
It does not seem nearly useful or used enough to warrant those complications.
Literally I have never seen any code using []= with a block.
If a block is useful the method should not be named with []= but something clearer so it's easy to pass a block without such contortions.

[nobu (Nobuyoshi Nakada)]

Whether or not that is useful, it is at least intentional as there are some tests for them.

[mame (Yusuke Endoh)]

• Status changed from Open to Assigned
• Assignee set to yui-knk (Kaneko Yuichiro)

Discussed at the dev meeting. @matz (Yukihiro Matsumoto) wanted to allow a[&b] and forbid a[&b] = c if the implementation is not overly cumbersome.

@yui-knk (Kaneko Yuichiro) What do you think?

Note: During the meeting, we found that the compilation of a[&b], c[&d] = e, f is apparently buggy. If it is difficult to prohibit the grammar, we need to fix this bug.

[nobu (Nobuyoshi Nakada)]

https://github.com/nobu/ruby/tree/ary_set-block

[nobu (Nobuyoshi Nakada)]

• Status changed from Assigned to Closed

Applied in changeset git|df5ef282337764508a1e1d93459d7a280e46647c.

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[Bug #19918] Reject block passing in index