小编mad*_*tap的帖子

为什么地图和关键字都有一个带有默认参数的额外arity,而set则没有？

这是实施细节还是具体的设计决策？

({:a 2} :b :not-found) ;;=> :not-found

(:b {:a 2} :not-found) ;;=> :not-found

;; This seems counter intuitive.
(#{:a} :b :not-found) ;;=> clojure.lang.ArityException

(:b #{:a} :not-found) ;;=> :not-found

我正在做railstutorial的草稿版本,当我尝试运行时,bundle exec rake test:models我收到此错误消息:

rake aborted!
Errno::EACCES: Permission denied - C:/Users/Alex/Desktop/Workspace/Rails/sample_
app/db/test.sqlite3
C:/Users/Alex/Desktop/Workspace/Rails/sample_app/test/test_helper.rb:3:in `<top
(required)>'
C:/Users/Alex/Desktop/Workspace/Rails/sample_app/test/helpers/application_helper
_test.rb:1:in `<top (required)>'
Tasks: TOP => test:run => test:units
(See full trace by running task with --trace)

使用--trace:

** Invoke test (first_time)
** Execute test
** Invoke test:run (first_time)
** Invoke test:units (first_time)
** Invoke test:prepare (first_time)
** Execute test:prepare
** Execute test:units
rake aborted!
Errno::EACCES: Permission denied - C:/Users/Alex/Desktop/Workspace/Rails/sample_
app/db/test.sqlite3
C:/RailsInstaller/Ruby2.0.0/lib/ruby/2.0.0/fileutils.rb:1432:in `unlink'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/2.0.0/fileutils.rb:1432:in `block in remove
_file'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/2.0.0/fileutils.rb:1440:in `platform_suppor …

我正在尝试cl-format用来格式化钱.我想要(f 12345.555) ;=> "12,345.56".我得到格式字符串的小数,"~$"我得到逗号分隔符"~:D".我如何组合它们？

我在excel中的数据形状如下:

A       B  C  D
"foo"   5  3  1
"foo"   2  4  5
"foo"   5  5  5
"bar"   1  2  3
"bar"   4  5  7

我想知道在B列,C或D列中的A列和5列中有多少行包含"foo".

换句话说,我想要以下公式=COUNTIFS(A1:A5;"foo";B1:B5;5;C1:C5;5;D1:D5;5),但是B,C和D范围or是一起编辑而不是and'ed.使用excel公式有一个简单的方法吗？

我与投票,评论和帖子有多态关联,如下所示:

class Vote < ActiveRecord::Base
  belongs_to :voteable, polymorphic: true
end

class Post < ActiveRecord::Base
  has_many :votes, as: :voteable
end

class Comment < ActiveRecord::Base
  has_many :votes, as: :voteable
end

当我点击upvote链接时,我发送voteable_type并voteable_id在params中.在投票控制器中,我想使用这两个字符串找到可投票对象,但我发现的唯一解决方案是eval.我认为从参数中评估字符串并不是一个好主意.

class VotesController < ApplicationController
  def find_voteable
    @voteable = eval("#{params[:vote][:voteable_type]}.find(params[:vote][:voteable_id])")
  end
end

有关如何按类名和ID查找ActiveRecord对象的任何建议？或者,有没有更好的方法来做这个不发送参数中的东西？