在Rails插件中擴展核心類無法正常工作

Question

在#PLUGIN/lib/#PLUGIN內部，我插入了以下內容：

String.class_eval do
  def to_squawk
    "squawk! #{self}".strip
  end
end

當我嘗試在Rails Console中進行測試時。 我收到以下錯誤： NoMethodError: undefined method “測試字符串”的NoMethodError: undefined method to_squawk'：String`

Loading development environment (Rails 4.2.0.beta2)
2.1.3 :001 > "test string".to_squawk
NoMethodError: undefined method `to_squawk' for "test string":String
  from (irb):1
  from /Users/fab/.rvm/gems/ruby-2.1.3/gems/railties-4.2.0.beta2/lib/rails/commands/console.rb:110:in `start'
  from /Users/fab/.rvm/gems/ruby-2.1.3/gems/railties-4.2.0.beta2/lib/rails/commands/console.rb:9:in `start'
  from /Users/fab/.rvm/gems/ruby-2.1.3/gems/railties-4.2.0.beta2/lib/rails/commands/commands_tasks.rb:68:in `console'
  from /Users/fab/.rvm/gems/ruby-2.1.3/gems/railties-4.2.0.beta2/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
  from /Users/fab/.rvm/gems/ruby-2.1.3/gems/railties-4.2.0.beta2/lib/rails/commands.rb:17:in `<top (required)>'
  from bin/rails:4:in `require'
  from bin/rails:4:in `<main>'

我在這里關注該教程： http : //guides.rubyonrails.org/plugins.html

有人知道這是什么問題嗎？

Answer 1

這是Rails指南中的代碼：

String.class_eval do
  def to_squawk
    "squawk! #{self}".strip
  end
end

這是您的代碼：

String.class_eval do
  def self.to_squawk
    "squawk! #{self}".strip
  end
end

看到不同？ 指南的代碼定義了String實例響應的實例方法（即"foo".to_squawk # => "squawk! foo" ），但是您的代碼及其雜散的self定義了String類響應的類方法（即String.to_squawk # => "squawk! String" ）。