Rails console 'y' helper returns NameError rather than yaml-formatting output

问题

I'm trying to use y object in Rails 3.2.6/Ruby 1.9.3 console to get nicely formatted yaml output for an ActiveRecord object, but for some reason it isn't working for me. I've used it in the past, but somewhere along the way it broke. I get the following output when I try:

NameError: undefined local variable or method `yaml' for main:Object

回答1:

The y method is actually an extension to the Kernel object put in place by the Syck YAML parser/emitter. Here are the last few lines of lib/ruby/1.9.1/syck.rb:

module Kernel
    def y( object, *objects )
        objects.unshift object
        puts( if objects.length == 1
                  YAML.dump( *objects )
              else
                  YAML.dump_stream( *objects )
              end )
    end
    private :y
end

By default, Ruby 1.9.3 uses the Psych parser/emitter instead of Syck (I can only presume they're pronounced differently), and Psych doesn't declare such a method.

If you really loved y, you can simply use Syck instead of Psych in the console:

Loading development environment (Rails 3.2.5)
1.9.3p194 :001 > y 'hello'
NoMethodError: undefined method 'y' for main:Object
1.9.3p194 :002 > YAML::ENGINE.yamler = 'syck'
"syck"
1.9.3p194 :003 > y 'hello'
--- hello
nil

I'll also use this chance to plug awesome_print, which does for basically everything what y does for YAML.