rescue.rb

class MessageMatcher < Module
  def initialize(pattern)
    @pattern = pattern
  end

  def ===(exception)
    exception.message.match?(@pattern)
  end
end

def message_matcher(msg)
  Module.new.tap do |mod|
    mod.define_singleton_method(:===) { |exc| exc.message.match?(msg) }
  end
end

begin
  raise 'Foo'
rescue MessageMatcher.new(/foo/i) => e # rescue message_matcher(/foo/)
  puts "rescued #{e}"
end