gistfile1.txt

ruby % rvm use 1.9.2
Using /Users/qrush/.rvm/gems/ruby-1.9.2-p136

ruby % irb
ruby-1.9.2-p136 :001 > a = []
 => [] 
ruby-1.9.2-p136 :002 > a.push(3,)
 => [3] 

ruby % rvm use ree  
Using /Users/qrush/.rvm/gems/ree-1.8.7-2010.02

ruby % irb
ree-1.8.7-2010.02 :001 > a = []
 => [] 
ree-1.8.7-2010.02 :002 > a.push(3,)
SyntaxError: compile error
(irb):2: syntax error, unexpected ')'
        from (irb):2
        from :0

This has always worked for arrays ([3,]). Ruby 1.9 just extends it to parameter lists.