Pit Capitain wrote:
> Hi,
>
> Dan Berger's recent thread about using UnboundMethod#bind to redefine an
> existing method reminded me of a problem I still have:
>
>    What is the fastest way to redefine an existing method?
>
> With "fast" I don't mean the process of redefining the method, but the
> time it takes to actually call the new implementation.
>
> With "redefining an existing method" I mean changing the implementation
> of an existing method so that in the new implementation it is possible
> to call the old one and use its return value.
>
> I've seen many different techniques in the past here on ruby-talk, but I
> haven't looked at the tradeoffs. I promise to write a page on the ruby
> garden wiki with the results.
>
> Regards,
> Pit

A cut is going to be just about the fastest I think since it is
essentially a subclass, although defining the "wrapping" method
requires a bit of additional overhead. Alias certainly has the least
overhead. I imagine before and after wraps as matz has suggested for
Ruby 2.0 would be faster, albiet they are more limited in capability
than cuts.

Keep in mind that every "wrap" will have a benchmark greater than the
orginal by neccessity b/c includes the originals call --so what's
really of interest is the difference from the original. Consdiering
that it is clear what the fastest way would be. To literally extract
the source code of the oringal method and wrap it via string
manipulation and eval the result as the new method. Of course, that's
not all that practical -- for starters I think you would need something
like ParseTree to even pull it off.

Anyway here's Ara's benchmarks with cuts/subclass added:

#
# Alias
#
class HashUsingAlias < Hash
    alias :old_hset :[]=

    def []=(key, value)
      self.old_hset(key, value)
    end
end

#
# Bind
#
class HashUsingBind < Hash
    hset = self.instance_method(:[]=)

    define_method(:[]=) do |key, value|
      hset.bind(self).call(key, value)
    end
end

#
# Override
#
require 'override'
class HashUsingOverride < Hash
   override('[]='){ def []=(k,v) super end }
end

#
# Subclass
#
class HashUsingSubClass < Hash
  def []=(k,v)
    super
  end
end

#
# Cut (pure ruby meta-hacking version)
#
require 'facets/more/cut'
class HashUsingCut < Hash; end

cut :HashUsingCutAspect < HashUsingCut do
  def []=(k,v); super; end
end

require "benchmark"
def bm_report bm, title, hash_class
   hash = hash_class.new
   bm.report title do
     100_000.times do
       hash[ 1 ] = 1
     end
   end
end

Benchmark.bmbm do |bm|
   bm_report bm, "original", Hash
   bm_report bm, "alias", HashUsingAlias
   bm_report bm, "bind", HashUsingBind
   bm_report bm, "override", HashUsingOverride
   bm_report bm, "subclass", HashUsingSubClass
   bm_report bm, "cut", HashUsingCut
end


Rehearsal --------------------------------------------
original   0.100000   0.020000   0.120000 (  0.125107)
alias      0.180000   0.030000   0.210000 (  0.226911)
bind       0.460000   0.050000   0.510000 (  0.525037)
override   0.590000   0.030000   0.620000 (  0.630301)
subclass   0.170000   0.030000   0.200000 (  0.210436)
cut        0.170000   0.030000   0.200000 (  0.210003)
----------------------------------- total: 1.860000sec

               user     system      total        real
original   0.100000   0.010000   0.110000 (  0.123498)
alias      0.170000   0.040000   0.210000 (  0.224580)
bind       0.480000   0.030000   0.510000 (  0.529366)
override   0.570000   0.050000   0.620000 (  0.626580)
subclass   0.170000   0.030000   0.200000 (  0.214458)
cut        0.170000   0.030000   0.200000 (  0.209727)