From: Erwin Abbott <erwin.abbott@...>
Date: 2007-06-11T02:05:56+09:00
Subject: Re: Overloading Array Subtraction operator

On 6/10/07, Erwin Abbott <erwin.abbott@gmail.com> wrote:
> Yes, I responded hastily. The rdocs for Array#- don't say how objects
> are compared so I made a bad assumption. I only meant to convey it
> wasn't being done by comparing values.

... at least with the array of Hashes, Hash#hash is used and not
Hash#== or some value based comparison. I'm not sure how it's done
with Strings or Fixnums, I'd have to check the source code probably.
Check it out with the profiler:

$ ruby -rprofile -e '[{:a=>3}] - [{:b=>0,:a=>0}]'
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
  0.00     0.00      0.00        2     0.00     0.00  Kernel.hash
  0.00     0.00      0.00        1     0.00     0.00  Array#-
  0.00     0.01      0.00        1     0.00    10.00  #toplevel

$ ruby -rprofile -e '%w[a b c] - %w[b d e f]'
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
  0.00     0.00      0.00        1     0.00     0.00  Array#-
  0.00     0.01      0.00        1     0.00    10.00  #toplevel

$ ruby -rprofile -e '[1,2,3] - [0,3,5]'
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
  0.00     0.00      0.00        1     0.00     0.00  Array#-
  0.00     0.01      0.00        1     0.00    10.00  #toplevel

Regards,

Erwin