Issue #5558 has been updated by mame (Yusuke Endoh).

Status changed from Open to Assigned
Assignee set to matz (Yukihiro Matsumoto)

This behavior is certainly intended.  See [ruby-core:5161].

There is another example that behavior changes whether it is 
debug mode or not: Thread#abort_on_exception.

    Thread.new { raise }
    sleep 1

The above will terminate normally without -d.
But it will blow up with -d.
So, we should know that -d affects the behavior, IMO.

-- 
Yusuke Endoh <mame / tsg.ne.jp>
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Feature #5558: String#% strange arity errors
https://bugs.ruby-lang.org/issues/5558#change-25247

Author: trans (Thomas Sawyer)
Status: Assigned
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: 
Target version: 


When the number of arguments do not match the number of % parameters, the String#% method has some odd behavior.

When too many, it seems to work fine, ignoring the extra arguments.

  "%s" % [1,2]  #=> "1"

But if `$DEBUG = true`,

  "%s" % [1,2]  #=> ArgumentError: too many arguments for format string

That doesn't seem right. Is it an error or isn't it?

For too few arguments it is always an error:

  "%s" % []   #=> ArgumentError: too few arguments

Personally, I think it should use '' for missing arguments. That would make it more flexible in practice.

I consider the first $DEBUG issue a bug, and the later a feature. But I'll just call it a feature altogether to make things easier.



-- 
http://bugs.ruby-lang.org/