b.rb

# -- coding: utf-8

require "kyotocabinet"

class Stash
  include Enumerable

  def initialize(&block)
    @buf = []
    @filter = block
  end

  def each(&block)
    @buf.each{|v| block.call(v)}
  end

  def visit_full(key, value)
    @buf << key if @filter.call(key, value)
    KyotoCabinet::Visitor::NOP
  end
end

KyotoCabinet::DB.process('bar.kct') {|db|
  1.upto(100){|v|
    db[v.to_s] = v.to_s + "-value"
  }

  visitor = Stash.new{|k,v|
    k.match(/3/)
  }
  db.iterate(visitor)

  p visitor.take(2).map{|k| db[k]}
}