28字节ruby代码带来的乐趣！

是的。你没有看错，这是我今天看到的代码：

def p.method_missing*_;p;end

第一次看，还是没有看的全明白。然后咱们来个格式化后的版本：
class NilClass
 def method_missing *_
    nil
 end
end

别钻牛脚尖，非要一个字符字符对，看中间精华部分。此代码的作用是针对实例对象类如@some_hash，是个hash,
你想得到key=>value值时，出现nil时，提供的解决办法。

你可能希望这样的代码：
if @some_hash[:some_key] # good looking version
 # do something with @some_hash[:some_key]
end

但如果@some_hash是nil，上面的代码就会出exception了。
你不得不这么写：
if @some_hash && @some_hash[:some_key] # correct version
  # do something with @some_hash[:some_key]
end

再来一个完整的代码实例：

# Egocentric nil
# code by Yohan, slightly edited and comments by me

# start ego mode block, usage:
# catch_nil do
#   if @some_hash[:some_key].to_formatted_array[3]
#     # do something
#   end
# end
def catch_nil(&block)
  # grip methods
 ori_method_missing   = NilClass.instance_method(:method_missing)
  catch_method_missing = NilClass.instance_method(:catch_method_missing)
  # activate ego mode
 NilClass.send :define_method, :method_missing, catch_method_missing
  # run code
 yield
ensure
 # no matter what happens: restore default nil behaviour
 NilClass.send :define_method, :method_missing, ori_method_missing
end
#alias :egonil :catch_nil # ;)

# this is the ego nil
class NilClass
  def catch_method_missing(m, *args, &block)
    nil
 end
end

不管怎么说，真的很优雅。ruby is awesome!

详细看这里：

The 28 Bytes of Ruby Joy!

--
tommy xiao
E-mail: xiaods(AT)gmail.com

use jruby+sinatra+jfreechart build StackedBar graph! - Series 1

FYI,jruby is now 1.5.1, i want to build gpaph service.so i want to familiar with jruby and jfreechart api. this is blow doc is my practice notes.any feedback welcome.

first step:

use jruby+jetty+sinatra stack:

http://github.com/vvilhonen/Jetty-jruby-sinatra-skeleton

only git clone done.you will have done this stack in local

second step:

create your rb file:

charting.rb

==========

require 'rubygems'

require 'sinatra'

require 'java'

import 'org.jfree.data.category.DefaultCategoryDataset'

class DefaultCategoryDataset

  class Inner

    def initialize(dataset, row)

      @dataset, @row = dataset, row.to_s

    end

    # a value of nil can call 'removeValue'

    def []=(column, value)

      @dataset.addValue value.to_java(:int), @row, column.to_s

    end

    def populate(hash)

      hash.each_pair do |column, value|

        @dataset.addValue value.to_java(:int), @row, column.to_s

      end

    end

  end

  def [](row)

    Inner.new self, row

  end

end

module Graph

  class StackedBar

    include_class 'java.io.File'

    include_class 'org.jfree.chart.ChartUtilities'

    include_class 'org.jfree.chart.JFreeChart'

    include_class 'org.jfree.data.category.DefaultCategoryDataset'

    include_class 'org.jfree.chart.ChartFactory'

    include_class 'org.jfree.chart.plot.PlotOrientation'

    def initialize(width=600, height=400, data=[])

      @width = width

      @height = height

      dataset = create_sample_data() if data.empty?

      @chart = create_chart(dataset)

    end

    def render_to_file(filename, format="png")

      puts "Rendering graph to #{filename}"

      javafile = java.io.File.new(filename)

      ChartUtilities.saveChartAsPNG(javafile, @chart, @width, @height)

    end

    private

    def create_sample_data

      # This also allows symbols as well as strings

      dataset = DefaultCategoryDataset.new

      dataset[:Submitted].populate(:A => 1, :B => 2, :C => 3)

      dataset[:Assigned].populate(:A => 1, :C => 1)

      dataset["In-work"].populate(:A => 3, :C => 3)

      dataset[:InVerfication][:A] = 1

      dataset[:Delivered][:A] = 2

      dataset[:Rejected][:B] = 1

      dataset[:Closed][:B] = 1

      dataset["On-hold"][:C] = 2

      dataset

    end

    def create_chart(dataset)

      chart = ChartFactory.createStackedBarChart("XYZ's Development Projects",

                                                 "Project Name", 

                                                 "Hours", 

                                                 dataset, 

                                                 PlotOrientation::VERTICAL, 

                                                 true, 

                                                 true, 

                                                 false)

      return chart    

    end

  end # class StackedBar  

end # class Graph

get '/' do

  sb = Graph::StackedBar.new

  @pp = "stacked_bar.png"

  img_pub = "public/images/"

  sb.render_to_file(img_pub+@pp)

  erb :graph

end

fix some expired function and modified from http://kfahlgren.com/blog/2007/07/12/stacked-bar-charts-in-jruby-using-jfreechart/

--
tommy xiao
E-mail: xiaods(AT)gmail.com