Ruby » Backport187

Backport #3938

Updated by jeremyevans0 (Jeremy Evans) almost 5 years ago

=begin 
  
  Given an Enumerable object that has an element which is an Array, when an Enumerable method which takes a block (#map, #detect, etc) is called on that object and given a Method as its block, Ruby will incorrectly compare the length of the Array to the arity of the Method.  
 
    def Object.onearg(arg) 
      arg 
    end 
    amethod = Object.method(:onearg) 
    aproc = proc{|arg| arg} 
 
  amethod and aproc both have arity of 1. they should generally behave the same. but, they behave differently when given as a block to Enumerable methods, with amethod behaving incorrectly when the Enumerable in question contains an array:  
 
    >> [[1, 2]].detect(&amethod) 
    ArgumentError: wrong number of arguments (2 for 1) 
 
  this seems to incorrectly compare the length of the element [1, 2] to the arity of amethod, even though it's passing one argument (the array [1, 2]) to amethod.  
 
  the Proc behaves correctly: 
 
    >> [[1, 2]].detect(&aproc) 
    => [1, 2] 
 
  this does not compare the element's length to the arity of aproc, and so works fine.  
 
  Giving the Method as a block works fine when the arity happens to be the same as the length of the element which is an array: 
 
    > [[1]].detect(&amethod) 
    => [1] 
 
  Even though it is passed the whole array (seen in the return value), and not the element of the array.  
 
  File is attached to minimally reproduce, and its output is: 
 
  [1, 2] 
  [1] 
  methodarity.rb:10:in `onearg': wrong number of arguments (2 for 1) (ArgumentError) 
 	 from methodarity.rb:10:in `to_proc' 
 	 from methodarity.rb:7:in `detect' 
 	 from methodarity.rb:10:in `each' 
 	 from methodarity.rb:10:in `detect' 
 	 from methodarity.rb:10 
 
 
  Tested on: 
  ruby 1.8.6 (2009-06-08 patchlevel 369) [universal-darwin9.0] 
  ruby 1.8.6 (2010-02-05 patchlevel 399) [i686-darwin9.8.0]  
  ruby 1.8.7 (2009-06-12 patchlevel 174) [i686-darwin9.8.0] 
  ruby 1.8.7 (2010-06-23 patchlevel 299) [i686-darwin9.8.0]  
  ruby 1.8.6 (2007-09-24 patchlevel 111) [i386-mswin32] 
  ruby 1.8.6 (2010-02-04 patchlevel 398) [i386-mingw32] 
  ruby 1.8.7 (2010-01-10 patchlevel 249) [i386-mingw32] 
 
  Behaves correctly in ruby 1.9.*. 
 
 =end 
 

Back