From: Colin Bartlett <colinb2r@...>
Date: 2010-09-29T00:15:38+09:00
Subject: Re: copying a matrix.

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On Tue, Sep 28, 2010 at 7:05 AM, Brian Candler <b.candler@pobox.com> wrote:

> John Smith wrote:
> > How can I create an array copy that
> > does not reference the same object...
> > I have tried this without luck.
> > m2 = m.map { |e| e }
>
> Try:
>  m2 = m.map { |e| e.dup }


or maybe use:
m = [ "a", nil, true, false, 1, 2.0 ]
m2 = m.map { |e| e.dup rescue e }

I've wondered in the past why there isn't a dup or clone alternative which
for nil, true, false, Integer, Floats (anything else?) just returns the
object itself.

Is there any easy way of telling whether an object will respond to dup or
clone?
For all those objects listed above which won't dup or clone
  obj.respond_to?(:dup) #=> true on my computer

If the OP needs more than 2 levels of dups, this may be a case for more
general recursion, discussed here
  http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/360651
prompted by this thread:
  http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/360275


*** ruby 1.9.1p243 (2009-07-16 revision 24175) [i386-mingw32]

m = [ "a", nil, true, false, 1, 2.0 ]
m2 = m.map { |e|
    begin
      e.dup
    rescue
      puts "#=> dup of #{e.inspect} #=> #{$!.inspect}"
      puts "#=> #{e.respond_to?(:dup)} #{e.respond_to?(:clone)}"
      e
    end
}

#=> dup of nil #=> #<TypeError: can't dup NilClass>
#=> true true
#=> dup of true #=> #<TypeError: can't dup TrueClass>
#=> true true
#=> dup of false #=> #<TypeError: can't dup FalseClass>
#=> true true
#=> dup of 1 #=> #<TypeError: can't dup Fixnum>
#=> true true
#=> dup of 2.0 #=> #<TypeError: allocator undefined for Float>
#=> true true

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