Category Ruby, | {:web=>:wxianfeng}

ruby string to class

Posted by wxianfeng Thu, 17 Nov 2011 09:53:00 GMT

环境:ruby 1.9.2

有这样一个需求，给你任意一个字符串，把它转化为类,网上大多数的解决办法是下面三种:

Kernel.const_get(:User) # Object.const_get(:User)
eval(’User’)
‘User’.constantize

但是上面三种方法, 这个 User 事先必须是初始化的,不然会报错，如下:

Object.const_get(:User) # uninitialized constant User (NameError)

所以需要加个判断这个 Class 有没有初始化，没有的话再set 一个Class

require "rails/all"

def Kernel.const_missing(name)
  Object.const_set(name,Class.new)
end
#p Kernel.const_get("baoxiaos".to_sym) # wrong constant name baoxiaos (NameError)
p Kernel.const_get("baoxiaos".classify.to_sym) # Baoxiao , const的首字母必须大写
p Kernel.constants # []
p Object.constants.include?(:UBaoxiao) # true

刚开始把这个 const 定义在 Object 里:

require "rails/all"

def Object.const_missing(name)
  Object.const_set(name,Class.new)
end

#p Object.const_get("baoxiaos".to_sym) # wrong constant name baoxiaos (NameError)
p Object.const_get("baoxiaos".classify.to_sym)

发现用在 rails 中后 , rails 处处报错，可能怪我重写了 Object.const_missing 导致的 ……..

上面方法的原理是当找不到 const的时候执行了

  Object.const_set(name,Class.new)

那么 name 就变成是 Class 的实例了 , 为什么定义在 Kernel 中的 const_missing ，Object 也可以访问到，需要注意 Object,Kernel 之间的关系,Object 是 inluce Kernel 的,如下:

class Object
include Kernel
end

SEE:

http://niczsoft.com/2010/01/string-to-class-in-ruby-on-rails/
http://www.ruby-forum.com/topic/96222

Read full article no comments

homebrew install imagemagick

Posted by wxianfeng Sat, 10 Sep 2011 14:02:00 GMT

环境:mac os x lion
homebrew是用ruby写的脚本，发现和rvm极其相似

安装 homebrew

>/usr/bin/ruby -e "$(curl -fsSL https://raw.github.com/gist/323731)"

安装imagemagick

>brew install imagemagick

安装到libtiff 库时出错

curl: (7) couldn't connect to host
Error: Failure while executing: /usr/bin/curl -f#LA Homebrew\ 0.8\ (Ruby\ 1.8.7-249;\ Mac\ OS\ X\ 10.7.1) ftp://ftp.remotesensing.org/pub/libtiff/tiff-3.9.5.zip -o /Users/wangxianfeng/Library/Caches/Homebrew/libtiff-3.9.5.zip

fixed ：

>/usr/bin/curl http://download2.osgeo.org/libtiff/tiff-3.9.5.zip -o ~/Library/Caches/Homebrew/libtiff-3.9.5.zip

再次安装:

>brew install imagemagick

最后测试安装成功：

wxianfeng:inono wangxianfeng$ convert --version
Version: ImageMagick 6.7.1-1 2011-09-10 Q16 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2011 ImageMagick Studio LLC
Features: OpenMP

可以查看出brew安装了下面的库：

wxianfeng:inono wangxianfeng$ brew list
imagemagick jasper jpeg libtiff little-cms

see:
https://github.com/mxcl/homebrew/wiki/installation
https://github.com/mxcl/homebrew/pull/5168

Read full article no comments

北京 798 Ruby/Rails 活动

Posted by wxianfeng Sat, 30 Jul 2011 06:36:00 GMT

时间: 2011-07-24
收获:
发现北京ROR的公司不是一般的多,签到单上看到N多公司,技术上没有太大收获,都是介绍性的,没有实战性的,内容主要涉及: mirah , Mongodb,Erlang,Grape

进程:http://www.surveymonkey.com/s/MSY2L7T

PS : 798 很好玩,很有艺术特色

现场:

798 入口

Ruby活动地方

Rails rumble 创始人

现场job board

现场

清一色老外,清一色Mac

介绍Mirah

798

Read full article no comments

项目寻人

Posted by wxianfeng Mon, 14 Feb 2011 03:19:00 GMT

公司项目寻人,美工 + Ruby + Java + Flex + Javascript 工程师

招聘帖:

http://chinaonrails.com/topic/view/4746.html

http://www.oschina.net/bbs/thread/15953

Read full article no comments

ruby rake tips

Posted by wxianfeng Wed, 26 Jan 2011 06:59:00 GMT

环境:ruby 1.9.2 + rake 0.8.7 + rails 3.0.3

今天在写 rake 文件，提示我没找到 model Class，问题在于我没加 => :environment , 那为什么加上 => :environment 就可以了 , 研究了下rake:

task :test => :environment do 
end

其中后面的 :environment 也是一个 task ，也就是说在执行 test 这个 task 之前会执行 :environment 这个 task，有点像rails controller 中的 before_filter ,那么 :environment 这个task 定义在什么地方，rails project中也没有啊。。。，定义在 rails 源码中了，你在你的project下执行 rake environment 不会报错的

wxianfeng@ubuntu:/usr/local/system/projects/entos/ent_os$ rake environment --trace 
(in /usr/local/system/projects/entos/ent_os)
** Invoke environment (first_time)
** Execute environment

不过也看不到输出什么信息，因为只是加载了运行环境而已 ,那么从哪里执行的，定义在 project 下 Rakefile 中了

# Add your own tasks in files placed in lib/tasks ending in .rake,
# for example lib/tasks/capistrano.rake, and they will automatically be available to Rake.

require File.expand_path('../config/application', __FILE__)
require 'rake'

EntOs::Application.load_tasks

继续跟踪 load_tasks:

最后找到了 task environment

   def initialize_tasks

      require "rails/tasks"

      task :environment do

        $rails_rake_task = true

        require_environment!

      end

    end

全部文件 here

所以加载了 environment 也就可以找到 model Class 了

总结:

1,rake 命名格式

rakefile, Rakefile, rakefile.rb, Rakefile.rb 都可以，常用 Rakefile

另外 rails 中使用的话，还可以使用 .rake 后缀的文件

2,设置命名空间

namespace :test do
end

3,设置默认task

task :default => ["test"]

可以指定多个 task,执行 rake 后，默认调用的是 default task

4，指定task执行顺序

task :test => [:hello,:world]

5,查看rake 任务

rake -T  
rake --tasks
rake -T db: # 查看db打头的task

6,跟踪task

rake test --trace

更多 options

wxianfeng@ubuntu:/usr/local/system/projects/entos/ent_os$ rake -h
rake [-f rakefile] {options} targets...

Options are ...
    -C, --classic-namespace          Put Task and FileTask in the top level namespace
    -D, --describe [PATTERN]         Describe the tasks (matching optional PATTERN), then exit.
    -n, --dry-run                    Do a dry run without executing actions.
    -e, --execute CODE               Execute some Ruby code and exit.
    -p, --execute-print CODE         Execute some Ruby code, print the result, then exit.
    -E, --execute-continue CODE      Execute some Ruby code, then continue with normal task processing.
    -I, --libdir LIBDIR              Include LIBDIR in the search path for required modules.
    -P, --prereqs                    Display the tasks and dependencies, then exit.
    -q, --quiet                      Do not log messages to standard output.
    -f, --rakefile [FILE]            Use FILE as the rakefile.
    -R, --rakelibdir RAKELIBDIR,     Auto-import any .rake files in RAKELIBDIR. (default is 'rakelib')
        --rakelib
    -r, --require MODULE             Require MODULE before executing rakefile.
        --rules                      Trace the rules resolution.
    -N, --no-search, --nosearch      Do not search parent directories for the Rakefile.
    -s, --silent                     Like --quiet, but also suppresses the 'in directory' announcement.
    -g, --system                     Using system wide (global) rakefiles (usually '~/.rake/*.rake').
    -G, --no-system, --nosystem      Use standard project Rakefile search paths, ignore system wide rakefiles.
    -T, --tasks [PATTERN]            Display the tasks (matching optional PATTERN) with descriptions, then exit.
    -t, --trace                      Turn on invoke/execute tracing, enable full backtrace.
    -v, --verbose                    Log message to standard output.
    -V, --version                    Display the program version.
    -h, -H, --help                   Display this help message.

DEMO:

wxianfeng@ubuntu:~/test/rake$ cat Rakefile 
desc "Default: test"
task :default => ["r:test"]

namespace :r do 
desc "test" 
task :test  do
        puts "test"
end

desc "test1"
task :test1 => :test do
        puts "test1" 
end

desc "test3"
task :test3 => :test4 do
        puts "test3" 
end 
end

SEE:

http://hi.baidu.com/%D0%C7203/blog/item/ebda2dd09f1d698ea1ec9c7a.html
http://guides.rubyonrails.org/command_line.html
http://ericzouthoughts.wordpress.com/2009/06/20/execute-shell-command-in-ruby-rake-task/

Read full article 2 comments

ruby Object#tap and Object#returning

Posted by wxianfeng Wed, 19 Jan 2011 16:29:00 GMT

今天在rails中使用 returning 的时候 log 打出warning:

Object#returning has been deprecated in favor of Object#tap

环境是 ruby 1.9.2 + rails 3.0.3

从warn上看是returning不建议使用，建议使用tap方法,那么tap方法和returning方法有什么不同

Object#tap 方法是 ruby1.8.7 以后加入的,Object#returning 方法是 rails添加的

rails 3.0.3 returning 源码:here

rails 2.3.5 returning源码:

class Object
  # Returns +value+ after yielding +value+ to the block. This simplifies the
  # process of constructing an object, performing work on the object, and then
  # returning the object from a method. It is a Ruby-ized realization of the K
  # combinator, courtesy of Mikael Brockman.
  #
  # ==== Examples
  #
  #  # Without returning
  #  def foo
  #    values = []
  #    values << "bar"
  #    values << "baz"
  #    return values
  #  end
  #
  #  foo # => ['bar', 'baz']
  #
  #  # returning with a local variable
  #  def foo
  #    returning values = [] do
  #      values << 'bar'
  #      values << 'baz'
  #    end
  #  end
  #
  #  foo # => ['bar', 'baz']
  #  
  #  # returning with a block argument
  #  def foo
  #    returning [] do |values|
  #      values << 'bar'
  #      values << 'baz'
  #    end
  #  end
  #  
  #  foo # => ['bar', 'baz']
  def returning(value)
    yield(value)
    value
  end

  # Yields <code>x</code> to the block, and then returns <code>x</code>.
  # The primary purpose of this method is to "tap into" a method chain,
  # in order to perform operations on intermediate results within the chain.
  #
  #   (1..10).tap { |x| puts "original: #{x.inspect}" }.to_a.
  #     tap    { |x| puts "array: #{x.inspect}" }.
  #     select { |x| x%2 == 0 }.
  #     tap    { |x| puts "evens: #{x.inspect}" }.
  #     map    { |x| x*x }.
  #     tap    { |x| puts "squares: #{x.inspect}" }
  def tap
    yield self
    self
  end unless Object.respond_to?(:tap)

  # An elegant way to factor duplication out of options passed to a series of
  # method calls. Each method called in the block, with the block variable as
  # the receiver, will have its options merged with the default +options+ hash
  # provided. Each method called on the block variable must take an options
  # hash as its final argument.
  # 
  #   with_options :order => 'created_at', :class_name => 'Comment' do |post|
  #     post.has_many :comments, :conditions => ['approved = ?', true], :dependent => :delete_all
  #     post.has_many :unapproved_comments, :conditions => ['approved = ?', false]
  #     post.has_many :all_comments
  #   end
  #
  # Can also be used with an explicit receiver:
  #
  #   map.with_options :controller => "people" do |people|
  #     people.connect "/people",     :action => "index"
  #     people.connect "/people/:id", :action => "show"
  #   end
  #
  def with_options(options)
    yield ActiveSupport::OptionMerger.new(self, options)
  end
  
  # A duck-type assistant method. For example, Active Support extends Date
  # to define an acts_like_date? method, and extends Time to define
  # acts_like_time?. As a result, we can do "x.acts_like?(:time)" and
  # "x.acts_like?(:date)" to do duck-type-safe comparisons, since classes that
  # we want to act like Time simply need to define an acts_like_time? method.
  def acts_like?(duck)
    respond_to? "acts_like_#{duck}?"
  end

end

可以看到 tap 方法也封装了，为了防止 ruby版本过低没有tap方法就添加Object#tap 方法,tap 和 returning本质是一样的，函数体都是调用block闭包,只不过returning需要传递一个参数给闭包,最后返回的就是这个参数,而 tap直接操作self指针,最后返回的也就是self

另外最新rails源码(>rails3.0.3)已经没有 returning方法了，所以以后最好都用tap方法

DEMO1:

require "rubygems"
require "active_support"
# Object#tap 是>ruby1.8.7 有的
# Object#returning 是Rails 封装的方法, rails3.X 已经不建议使用

# Object#tap 可以支持链式(chain)操作
(1..10).tap {
  |x| puts "original: #{x.inspect}"
}.to_a.tap {
  |x| puts "array: #{x.inspect}"
}.select {|x| x%2==0}.tap {
  |x| puts "evens: #{x.inspect}"
}.map {|x| x*x}.tap {
  |x| puts "squares: #{x.inspect}"
}

def object_tap
  {}.tap do |h| # => Hash.new.tap
    h[:a] = 1
    h[:b] =2
  end
end

p object_tap # {:b=>2, :a=>1}

def object_returning
  returning Hash.new do |h| # 注意这里不能用 {}  , 放在 returning 方法后面 当作成 block闭包了
    h[:a] = 1
    h[:b] = 2
  end  
end

p object_returning # {:b=>2, :a=>1}

DEMO2:

require "rubygems"
require "active_support"

class Hash  
  def shift_value_tap_self
    self.tap do |h|
      h.each { |k,v| v.shift if v.is_a?(Array) }
    end
  end
  def shift_value_tap
    {}.tap do |h|
      self.each { |k,v|  v.is_a?(Array) ? h[k] = v.shift : h[k] = v } 
    end
  end

  def shift_value_returning
    returning Hash.new do |h|
      self.each { |k,v|  v.is_a?(Array) ? h[k] = v.shift : h[k] = v } 
    end
  end
  def shift_value_returning_self
    returning self do |h|
      h.each { |k,v| v.shift if v.is_a?(Array) }
    end
  end
end

hsh = {"a"=>[1,2,3],"b"=>["g","f","w"],"c"=>"fuck_china"}
hsh1 = {"a"=>[1,2,3],"b"=>["g","f","w"],"c"=>"fuck_china"}
hsh2 = {"a"=>[1,2,3],"b"=>["g","f","w"],"c"=>"fuck_china"}
hsh3 = {"a"=>[1,2,3],"b"=>["g","f","w"],"c"=>"fuck_china"}
p hsh.shift_value_tap # {"a"=>1, "b"=>"g", "c"=>"fuck_china"}
p hsh1.shift_value_returning # {"a"=>1, "b"=>"g", "c"=>"fuck_china"}
p hsh2.shift_value_tap_self # {"a"=>[2, 3], "b"=>["f", "w"], "c"=>"fuck_china"}
p hsh3.shift_value_returning_self # {"a"=>[2, 3], "b"=>["f", "w"], "c"=>"fuck_china"}

SEE:
http://blog.rubybestpractices.com/posts/gregory/011-tap-that-hash.html
http://www.simonecarletti.com/blog/2010/09/rails-3-beware-the-tap-pattern/
http://fuliang.javaeye.com/blog/857163

Read full article no comments

ruby instance_variables

Posted by wxianfeng Tue, 11 Jan 2011 05:52:00 GMT

环境:ruby 1.9.2 + ubuntu 10.10

instance_variables 得到当前对象已经开辟内存空间的实例变量,疑惑在这里

class Foo

  attr_accessor :sex,:birthday  

end

p Foo.new.instance_variables # => []

刚开始不理解,怎么是空……..

后来想了想，因为 ruby 是动态的解释型的语言，如果没有给实例变量赋值的话，是不会开辟内存空间的，所以 instance_variables 只能得到已经开辟内存空间的实例变量，
但是如果是编译型的静态语言则不然，例如java ，实例变量声明了就会开辟内存空间了

DEMO1:

# ruby version : 1.9.2

class Foo

  attr_accessor :sex,:birthday # attr_accessor ruby里封装的method  

end

p Foo.new.instance_variables # => []

f = Foo.new
p f.sex #=> nil
f.sex = 'M' 
p f.instance_variables #=>  [:@sex]
p f.inspect # => "#<Foo:0x85ead8c @sex=\"M\">"

b = Foo.new
b.birthday = nil # 注意赋值为nil,也开辟了内存空间
p b.instance_variables # => [:@birthday]
p b.inspect # => "#<Foo:0x9dca358 @birthday=nil>"

DEMO2:

class Foo
  
  def initialize
    @name = 'wxianfeng'
  end

  def bar # => as getter method
    @name
  end

end

f = Foo.new
p f.instance_variables #=> [:@name]
p f.inspect #=> "#<Foo:0x8aa7c08 @name=\"wxianfeng\">"
p f.name # =>  undefined method `name' for #<Foo:0x99adf7c @name="wxianfeng">
p f.bar # => "wxianfeng"

ruby 源码:

    # obj.instance_variables    => array
    #
    #
    # Returns an array of instance variable names for the receiver. Note
    # that simply defining an accessor does not create the corresponding
    # instance variable.
    #
    #    class Fred
    #      attr_accessor :a1
    #      def initialize
    #        @iv = 3
    #      end
    #    end
    #    Fred.new.instance_variables   #=> ["@iv"]
    #
    #
    def instance_variables
      # This is just a stub for a builtin Ruby method.
      # See the top of this file for more info.
    end

SEE:
http://www.megasolutions.net/ruby/instance_variables-doesnt-return-unassigned-variables-68358.aspx

Read full article no comments

« Previous 1 2 3 Next »

{:web=>:wxianfeng}

Livesearch

Pages

Mp3

Categories

Archives

Syndicate

Tags

Links

Comments

capistrano 多机部署

正则 ?: 非捕获组

ruby string to class

homebrew install imagemagick

北京 798 Ruby/Rails 活动

ruby yaml 表示数组

项目寻人

ruby rake tips

ruby Object#tap and Object#returning

ruby instance_variables