这个肯定是 ActiveRecord 里的功能吧，一般 Ruby 类不支持这种写法的

#1 楼 @iBachue 是的，model 里面的，这个实现在哪个文件？

#2 楼 @kingwkb puts method(:"[]").source_location

#2 楼 @kingwkb ActiveRecord 的 base.rb 文件

# Returns the value of the attribute identified by <tt>attr_name</tt> after it has been typecast (for example,
# "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)).
# (Alias for the protected read_attribute method).
def [](attr_name)
  read_attribute(attr_name)
end

# Updates the attribute identified by <tt>attr_name</tt> with the specified +value+.
# (Alias for the protected write_attribute method).
def []=(attr_name, value)
  write_attribute(attr_name, value)
end

#4 楼 @iBachue https://github.com/rails/rails/blob/v3.2.13/activerecord/lib/active_record/base.rb 怎么没找到？

#5 楼 @kingwkb 前面贴给你的是 2.3 的路径 ActiveRecord 3.2 的路径是 lib/active_record/attribute_methods.rb

# Returns the value of the attribute identified by <tt>attr_name</tt> after it has been typecast (for example,
# "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)).
# (Alias for the protected read_attribute method).
def [](attr_name)
  read_attribute(attr_name)
end

# Updates the attribute identified by <tt>attr_name</tt> with the specified +value+.
# (Alias for the protected write_attribute method).
def []=(attr_name, value)
  write_attribute(attr_name, value)
end

#6 楼 @iBachue 非常感谢，一直没没懂这个神马意思，现在终于懂了

self[:xxx] 是因为这个类实现了#[]（*args）这个方法，实际上 self[:xxx] == self.[]（:xxx）