我已经看过很多开放式的例子，对于简单的事情来说似乎非常棒。但是，要求它在全局范围内定义一个名为open的方法，这真让我感到困扰。
这一点特别令人不安，因为在Rails 5控制台中进行了调整之后，似乎已经定义了一个名为open的方法：
irb(main):001:0> open
ArgumentError: wrong number of arguments (given 0, expected 1..3)
from (irb):1:in `initialize'
from (irb):1:in `open'
from (irb):1
from /Users/ahamon/.gem/ruby/2.3.0/gems/railties-5.0.0.beta3/lib/rails/commands/console.rb:65:in `start'
from /Users/ahamon/.gem/ruby/2.3.0/gems/railties-5.0.0.beta3/lib/rails/commands/console_helper.rb:9:in `start'
from /Users/ahamon/.gem/ruby/2.3.0/gems/railties-5.0.0.beta3/lib/rails/commands/commands_tasks.rb:78:in `console'
from /Users/ahamon/.gem/ruby/2.3.0/gems/railties-5.0.0.beta3/lib/rails/commands/commands_tasks.rb:49:in `run_command!'
from /Users/ahamon/.gem/ruby/2.3.0/gems/railties-5.0.0.beta3/lib/rails/command.rb:20:in `run'
from /Users/ahamon/.gem/ruby/2.3.0/gems/railties-5.0.0.beta3/lib/rails/commands.rb:18:in `<top (required)>'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:302:in `require'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:302:in `block in require'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:268:in `load_dependency'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:302:in `require'
from /Users/ahamon/code/signist/bin/rails:9:in `<top (required)>'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:296:in `load'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:296:in `block in load'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:268:in `load_dependency'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:296:in `load'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/commands/rails.rb:6:in `call'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/command_wrapper.rb:38:in `call'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application.rb:185:in `block in serve'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application.rb:156:in `fork'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application.rb:156:in `serve'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application.rb:131:in `block in run'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application.rb:125:in `loop'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application.rb:125:in `run'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application/boot.rb:18:in `<top (required)>'
from /Users/ahamon/.rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /Users/ahamon/.rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from -e:1:in `<main>'irb(main):002:0>
如果我继续require 'open-uri'，则返回值为true，我现在已经删除了之前的open，无论它是什么：
irb(main):002:0> require 'open-uri'
=> true
irb(main):003:0> open
ArgumentError: wrong number of arguments (given 0, expected 1+)
from /Users/ahamon/.rubies/ruby-2.3.0/lib/ruby/2.3.0/open-uri.rb:29:in `open'
from (irb):3
from /Users/ahamon/.gem/ruby/2.3.0/gems/railties-5.0.0.beta3/lib/rails/commands/console.rb:65:in `start'
from /Users/ahamon/.gem/ruby/2.3.0/gems/railties-5.0.0.beta3/lib/rails/commands/console_helper.rb:9:in `start'
from /Users/ahamon/.gem/ruby/2.3.0/gems/railties-5.0.0.beta3/lib/rails/commands/commands_tasks.rb:78:in `console'
from /Users/ahamon/.gem/ruby/2.3.0/gems/railties-5.0.0.beta3/lib/rails/commands/commands_tasks.rb:49:in `run_command!'
from /Users/ahamon/.gem/ruby/2.3.0/gems/railties-5.0.0.beta3/lib/rails/command.rb:20:in `run'
from /Users/ahamon/.gem/ruby/2.3.0/gems/railties-5.0.0.beta3/lib/rails/commands.rb:18:in `<top (required)>'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:302:in `require'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:302:in `block in require'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:268:in `load_dependency'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:302:in `require'
from /Users/ahamon/code/signist/bin/rails:9:in `<top (required)>'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:296:in `load'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:296:in `block in load'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:268:in `load_dependency'
from /Users/ahamon/.gem/ruby/2.3.0/gems/activesupport-5.0.0.beta3/lib/active_support/dependencies.rb:296:in `load'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/commands/rails.rb:6:in `call'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/command_wrapper.rb:38:in `call'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application.rb:185:in `block in serve'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application.rb:156:in `fork'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application.rb:156:in `serve'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application.rb:131:in `block in run'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application.rb:125:in `loop'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application.rb:125:in `run'
from /Users/ahamon/.gem/ruby/2.3.0/gems/spring-1.6.4/lib/spring/application/boot.rb:18:in `<top (required)>'
from /Users/ahamon/.rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /Users/ahamon/.rubies/ruby-2.3.0/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from -e:1:in `<main>'irb(main):004:0>
注意每个堆栈跟踪中指定的不同arity。
那么之前定义的open是什么？擦除是否安全？有没有办法在不定义全局方法的情况下使用open-uri？
答案 0 :(得分：5)
open是Kernel#open，而不是Rails。 open-uri换行Kernel#open：它检查目标是否为网址或知道#open，如果是，则处理它，如果不是，则将所有内容传递给真实Kernel#open。
因此，如果没有open-uri，网址不起作用，openable就不起作用，其他一切都不起作用。使用open-uri，URL工作，openable工作，其他一切都相同。在open-uri检查您的参数是否为URL或响应#open时，除了非常非常轻微的性能影响外，应该没有危险要求。