Ruby 零碎點

1. Ruby 中純數據結構 ( Struct 與 OpenStruct )

講一下它倆之間的區別:
Struct 需要開頭明確聲明字段; 而 OpenStruct 人如其名, 隨時可以添加屬性
Struct 性能優秀; 而 OpenStruct 差點, 具體的性能差距可看這裏:http://stackoverflow.com/questions/1177594/ruby-struct-vs-openstruct
Struct 是 Ruby 解釋器內置, 用 C 實現; 
OpenStruct 是 Ruby 標準庫, Ruby 實現

API 不同: Struct API 與 OpenStruct

2. 聯合索引 gem composite_primary_keys

3. Hash assert_valid_keys 白名單

4. 網頁服務器 pow 

5. instance_of?, is_a? Class

6. respond_to? 和 send, class_eval, instance_methods/define_method

http://ruby-china.org/topics/3434

7. method_missing，一個 Ruby 程序員的夢中情人 

    def method_missing(method, *args)
      if method.to_s =~ /(.*)_with_cent$/
        attr_name = $1
        if self.respond_to?(attr_name)
          '%.2f' % (self.send(attr_name).to_f / 100.00)
        else
          super
        end
      end
    end

  def self.method_missing(method_sym, *arguments, &block)
    if method_sym.to_s =~ /^n_(.*)$/
      find_by_process_class($1)
    else
      super
    end
  end

  def method_missing(meth, *args, &blk)
    # 支持 suspending? ending? init? force?
    if meth.to_s =~ /(.*)\?$/
      return is_status?($1)
    end
    # 支持 stat_to_init stat_to_suspending stat_to_ending stat_to_force
    if meth.to_s =~ /^stat_to_(.*)$/
      return trans_stat_to($1)
    end
    # 不要丟了super
    super
  end

8. config.middleware 通過 rake -T 可以查看

9. block/block_given? # yield if block_given?

10. 監視Rails進程內存泄漏的技巧

http://robbin.iteye.com/blog/307271
https://ruby-china.org/topics/15853
http://blog.linjunhalida.com/blog/ruby-memory-leak-debug/
http://blog.linjunhalida.com/blog/librr-debug-cpu-usage-high/

gem

https://github.com/binarylogic/memorylogic
https://github.com/noahd1/oink

11. # Excel Generator

gem 'spreadsheet', '~> 0.7.3'

  PROVINCE = %w{ 安徽  北京  福建  甘肅  廣東  廣西  貴州  海南  河北  河南  黑龍江 湖北 
      湖南  吉林  江蘇  江西  遼寧  內蒙古 寧夏  青海  山東  山西  陝西  上海 
      四川  天津  西藏   新疆  雲南  浙江  重慶 }
  MONTH = 1.upto(12).to_a

  def self.total_to_xls(year = '2012', opts = {})
    book = Spreadsheet::Workbook.new
    sheet1 = book.create_worksheet
    months = MONTH
    months = opts[:month].to_s.split(/,/) if opts[:month]

    fixed_row = months.collect{ |m| m.to_s + '月' }.insert(0, '')

    sheet1.row(0).concat(fixed_row)
    row1 = ['']
    (months.size - 1).times { row1 << ['用戶數', '金額', '訂單數'] }

    sheet1.row(1).concat(row1.flatten!)
    row = 2

    sheet1.row(row).insert(0, '全國')

    months.each_with_index do |m, i|
      sheet1.row(row).insert(i*3 + 1, self.monthly_users_count(m))
      sheet1.row(row).insert(i*3 + 2, self.monthly_amount(m))
      sheet1.row(row).insert(i*3 + 3, self.monthly_orders_count(m))     
    end

    PROVINCE.each do |province|
      row += 1
      sheet1.row(row).insert(0, province)
      months.each_with_index do |m, i|
        sheet1.row(row).insert(i*3 + 1, self.monthly_users_count_by_province(m, province))
        sheet1.row(row).insert(i*3 + 2, self.monthly_amount_by_province(m, province))
        sheet1.row(row).insert(i*3 + 3, self.monthly_orders_count_by_province(m, province))
      end   
    end

    path = "tmp/phone_recharge.xls"
    book.write path
    path
  end

12. Object#tap

params.tap {|p| p[:foo] = 'bar' }

13. Array#bsearch #select, reject, find

bsearch要求搜索的數組是排序過的

require 'benchmark'


data = (0..50_000_000)


Benchmark.bm do |x|
  x.report(:find) { data.find {|number| number > 40_000_000 } }
  x.report(:bsearch) { data.bsearch {|number| number > 40_000_000 } }
end


         user       system     total       real
find     3.020000   0.010000   3.030000   (3.028417)
bsearch  0.000000   0.000000   0.000000   (0.000006)

14. Enumerable#flat_map

```ruby
module CommentFinder
  def self.find_for_users(user_ids)
    users = User.where(id: user_ids)
    user.posts.map do |post|
      post.comments.map |comment|
        comment.author.username
      end
    end
  end
end
```


flatten


```ruby
module CommentFinder
  def self.find_for_users(user_ids)
    users = User.where(id: user_ids)
    user.posts.map { |post|
      post.comments.map { |comment|
        comment.author.username
      }.flatten
    }.flatten
  end
end
```


flat_map
```ruby
module CommentFinder
  def self.find_for_users(user_ids)
    users = User.where(id: user_ids)
    user.posts.flat_map { |post|
      post.comments.flat_map { |comment|
        comment.author.username
      }
    }
  end
end
```

15. Array.new with a Block

class Board
  def board
    @board ||= Array.new(8) { Array.new(8) { '0' } }
  end
end

16. <=>

def fix_minutes
  until (0...60).member? minutes
    @hours -= 60 <=> minutes
    @minutes += 60 * (60 <=> minutes)
  end
  @hours %= 24
  self
end