[ruby-core:82700] [Ruby trunk Bug#13879] [Not sure if a bug or not] case/when menus and trailing ', ' commas in when clauses

Issue #13879 has been updated by shevegen (Robert A. Heiler).


I forgot to add - I assume that the puts invocation may lead to
trigger the above behaviour. My main confusion is why the ',' 
placed matters, depending whether one does an assignment, or
invokes a method. I would have assumed that the first would
also lead to a syntax error or similar, but instead ruby works
just fine with it, so I am not sure if this is a bug or intended
behaviour.

----------------------------------------
Bug #13879: [Not sure if a bug or not] case/when menus and trailing ',' commas in when clauses
https://bugs.ruby-lang.org/issues/13879#change-66534

* Author: shevegen (Robert A. Heiler)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-linux]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
Hello,

I am not sure if the following is a bug or a feature.

    x = 'foobar'
    case x
    when 'a','b','c',
      x = 5
    end
    puts x

Works fine.

But this here:

    x = 'foobar'
    case x
    when 'a','b','c',
      puts 5
    end

Leads to this error:

    syntax error, unexpected tINTEGER, expecting keyword_do or '{' or '('

Is this deliberately so? My confusion is that case/when works fine
in one case, but leads to an error in another case. I am not
sure if it is a bug or not, but I believe in the first case,
the user may have not wanted to put a trailing ',' there and
simply forgot to remove it. That is actually how I found out about
this behaviour, since I have a huge case/when menu and sometimes
make typos when re-arranging entries, including such trailing ','
via copy/paste jobs. :)

If it is a bug then perhaps it can be fixed; if it is not a
bug, perhaps the official documentation could explain this
feature? Or perhaps if trailing ',' are not useful, there
may be a warning issued or something in the first case.

Anyway, I am just reporting this in case nobody knows about 
this - feel free to close this issue at any moment in time.

Thanks. 



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