Dynamic Exception Rescue in Ruby

dynamic.1.8.7.rb

#!/usr/bin/env ruby

def match_message(regexp)
  m = Module.new
  (class << m; self; end).instance_eval do
    define_method(:===) do |error|
      regexp === error.message
    end
  end
  m
end

begin
  raise StandardError, "Error message about a socket."
rescue match_message(/socket/) => error
  puts "Error #{error.class.name} matches /socket/; ignored."
end

dynamic.1.9.2.rb

#!/usr/bin/env ruby

def match_message(regexp)
  lambda{ |error| regexp === error.message }
end

begin
  raise StandardError, "Error message about a socket."
rescue match_message(/socket/) => error
  puts "Error #{error.class.name} matches /socket/; ignored."
end

dynamic.bench.rb

#!/usr/bin/env ruby

require 'benchmark'

def match_message192(regexp)
  lambda{ |error| regexp === error.message }
end
 
def match_message187(regexp)
  m = Module.new
  (class << m; self; end).instance_eval do
    define_method(:===) do |error|
      regexp === error.message
    end
  end
  m
end
 
Benchmark.bm do |x|
  x.report { 100_000.times{ match_message192(/socket/); } }
  x.report { 100_000.times{ match_message187(/socket/); } }
end

Just came across this. I tried the lambda approach and and getting TypeError in Ruby 2.1.1. It appears that this support has been removed :<

For anyone reaching this page from Google, the 1.8.7 version (straight out of Exceptional Ruby, buy it!) works fine in 2.1.2 :-)

It only appears to work on 1.9.x, something seems to have changed.