From: Marc-Andre Lafortune Date: 2012-02-14T15:22:06+09:00 Subject: [ruby-core:42593] [ruby-trunk - Bug #5694] Proc#arity doesn't take optional arguments into account. Issue #5694 has been updated by Marc-Andre Lafortune. Matz, what do you want us to do about ->(a=1){}.arity, in the 1.9.3 release and in the 2.0.0 version? Marc-Andr�� wrote in [ruby-core:41708]: > Hi, > > On Sun, Dec 11, 2011 at 10:51 PM, Yukihiro Matsumoto wrote: > > Hi, > > > > In message "Re: [ruby-core:41600] [ruby-trunk - Bug #5694] Proc#arity doesn't take optional arguments into account." > > ���� ����on Mon, 12 Dec 2011 11:30:26 +0900, Marc-Andre Lafortune writes: > > > > |Yukihiro Matsumoto wrote: > > |> We are not going to add incompatible changes to trunk, ... > > | > > |Could you please explain to me what difference you see between an "incompatible change" and any "bug fix"? > > > > Good point. ����It's whether the change makes difference from intention > > of the original designer. ... > > So do we agree that my patch is not an incompatible change? > > >����First I thought to keep the original arity > > behavior, but after investigating the behavior, both Method#arity and > > Proc#arity have weird corner cases. > > Apart from the one I'm pointing out (which is only present in Ruby > 1.9), what other corner cases are there? In particular, is there any > corner case in the 1.8 line? > > > My idea for new behavior is: > > > > ����* arity ignores all optional arguments > > ����* arity returns -n-1 if there's rest argument > > ����* where n is number of mandatory arguments > > > > Any opinion? > > Can you explain what would be gained by this new behavior, i.e. how is > this change more helpful than the current behavior? > > Also, can you explain why you consider that breaking the previous > behavior would be a good idea? > > A quick check for uses of `arity` in Rails reveal that the typical use > looks like "does this method use only 1 parameter or can it use more > than that?" > > Among other things, this change could break many Rails app. > > Moreover, Rails and any other gem using `arity` would have to jump > through hoops to maintain a compatible version with Ruby 1.8.7 (which > doesn't have the `parameters` method) and Ruby 1.9.2+. > > Finally, assuming you decide to go forward with this feature change > for Ruby 2.0, shouldn't the 1.9 line still be fixed with my patch to > be consistent? > > Thanks ---------------------------------------- Bug #5694: Proc#arity doesn't take optional arguments into account. https://bugs.ruby-lang.org/issues/5694 Author: Marc-Andre Lafortune Status: Open Priority: Normal Assignee: Yukihiro Matsumoto Category: core Target version: ruby -v: - Currently: ->(foo = 42){}.arity # => 0, should be -1 This is contrary to the documentation and to what we should expect from the equivalent method definition. Fixed in trunk, requesting backport for the 1.9 line. -- http://bugs.ruby-lang.org/