ruby best practices, ruby worst practices, harmful class variables. hardcoding into a corner, inheritance becomes restrictive, evails of evel(), resuce blind, method_missing

Ruby: ruby best practices, ruby worst practices.rb

require "pstore"
# pay attention to the psstore;s usage
# @@data = PStore,new("filename.store")
# @@data[id] = <Ruby Object> should be surrounded by @@data.transition do <> end block
class User

  def self.data
    @data ||= PStore.new("users.store") #in class method, @data means the class instance variable.
  end

  def self.add(id, user_data)
    data.transaction do #data here is interpreted as self.data method, which is class method, can be used directly without self prefix
      data[id] = user_data
    end
  end

  def self.find(id)
    data.transaction do
      data[id] or raise "User not found"
    end
  end
 
  def initialize(id)
    @user_id = id
  end

  def attributes
    self.class.find(@user_id)
  end

  def first_name
    attributes[:first_name]
  end

end


Prawn::Document.generate("hello.pdf") do
  text "Hello Prawn!"
end

module Prawn
  class Document
    def self.generate(filename,options={},&block)
      pdf = Prawn::Document.new(options,&block)
      pdf.render_file(filename)
    end
  end
end

class MyDocument < Prawn::Document
  def say_hello
    text "Hello MyDocument"
  end
end

MyDocument.generate("hello.pdf") do
  say_hello
end

module Prawn
  class Document
    def self.generate(filename,options={},&block)
      pdf = new(options,&block) #delete the determiner
      pdf.render_file(filename)
    end
  end
end

class A
  def self.foo # why not A.foo, becuase self, easy for refactor
    # ..
  end
  def self.bar
    # ..
  end
end

# the class include this module mixin.
# they can get the instnance method
# and class methods(class macro) defined in inner ClassMethods Module
# without need to use the extend
module GeneralLogger
  def log(msg)
    puts Time.now.strftime("%H:%M:  ") + msg
  end
  module ClassMethods
    def attr_logger(name)
      attr_reader name
      define_method("#{name}=") do |val|
        log ""
        instance_variable_set("@#{name}", val)
      end
    end
  end
  def self.included(host_class)
    host_class.extend(ClassMethods)
  end
end

class  Example
  include  GeneralLogger
  attr_logger  :value
end

ex  =  Example.new
ex.log("New  example  created")
ex.value  =  123
puts  "Value  is  #{ex.value}"
ex.value  =  "cat"
puts  "Value  is  #{ex.value}"


user1 = User.new("Gregory Brown", balance: 2500)
user2 = User.new("Arthur Brown", balance: 3300)
user3 = User.new("Steven Brown", balance: 3200)
f = Filter.new([user1, user2, user3])
f.search("balance > 3000") #=> [user2, user3]

class User
  def initialize(name, options)
    @name    = name
    @balance = options[:balance]
  end
  attr_reader :name, :balance
end
class Filter
  def initialize(enum)
    @collection = enum
  end
  def search(query)
    @collection.select { |e| e.instance_eval(query) }
  end
end

def search(query)
  raise "Invalid query" unless query =~ /^(\w+) ([><!]=?|==) (\d+)$/
  @collection.select { |e| e.instance_eval(query) }
end

def search(query)
  data = query.match(/^(?<attr>\w+) (?<op>[><!]=?|==) (?<val>\d+)$/)
  @collection.select do |e|
    attr = e.public_send(data[:attr])
    attr.public_send(data[:op], Integer(data[:val]))
  end
end

>> f.search("@balance = 0")

=begin
RuntimeError: Invalid query
        from (irb):33:in `search'
        from (irb):39
        from /Users/sandal/lib/ruby19_1/bin/irb:12:in `<main>'
=end

name = @user.first_name.capitalize rescue "Anonymous"
name = @user.first_name ? @user.first_name.capitalize : "Anonymous"
>> name = @user.a_fake_method.capitalize rescue "Anonymous"
=> "Anonymous"

class Prawn::Document
  # Provides the following shortcuts:
  #
  #    stroke_some_method(*args) #=> some_method(*args); stroke
  #    fill_some_method(*args) #=> some_method(*args); fill
  #    fill_and_stroke_some_method(*args) #=> some_method(*args); fill_and_stroke
  #
  def method_missing(id,*args,&block)
    case(id.to_s)
    when /^fill_and_stroke_(.*)/
      send($1,*args,&block); fill_and_stroke
    when /^stroke_(.*)/
      send($1,*args,&block); stroke
    when /^fill_(.*)/
      send($1,*args,&block); fill
    end
  end
end


def method_missing(id,*args,&block)
  case(id.to_s)
  when /^fill_and_stroke_(.*)/
    send($1,*args,&block); fill_and_stroke
  when /^stroke_(.*)/
    send($1,*args,&block); stroke
  when /^fill_(.*)/
    send($1,*args,&block); fill
  else
    super #当遇到不在此范围内（既传递给），传回给object#method_missing, 来raise一个异常
  end
end