[英]Strange behaviour when returning an array from class_eval'ed method
在Ruby 1.9.2中,我使用class_eval扩展了一个类。
def slugged(fields)
# assign string to variable only for easier debugging
method = <<-EOS
def slug_fields
#{ fields.is_a?(Array) ? fields.inspect : ":#{ fields }" }
end
EOS
class_eval method
end
只要字段是符号(例如,在slug_fields
slugged :name
, slug_fields
返回:name
), slug_fields
。
但是,调用slugged
以与阵列使得slug_fields
返回nil
(例如后slugged [:kicker, :headline]
, slug_fields
返回nil
)。
奇怪的是,调试slugged
,包含要创建的方法的字符串看起来与您期望的完全相同:
" def slug_fields\n [:kicker, :headline]\n end\n"
" def slug_fields\n :name\n end\n"
编辑:根据要求,对我来说比较完善的版本:
module Extensions
module Slugged
extend ActiveSupport::Concern
included do
before_validation { |record| record.slug ||= record.sluggerize }
end
module ClassMethods
def slugged(fields)
# assign string to variable only for easier debugging
method = <<-EOS
def slug_fields
#{ fields.is_a?(Array) ? fields.inspect : ":#{ fields }" }
end
EOS
class_eval method
end
end
module InstanceMethods
def sluggerize
fields = slug_fields
slug_string = case
when fields.is_a?(Array)
fields.map { |f| self.send(f) }.join('-')
else
self.send fields
end
slug_string.parameterize
end
end
end
end
class Article < ActiveRecord::Base
include Extensions::Slugged
slugged [:kicker, :headline]
end
class Station < ActiveRecord::Base
include Extensions::Slugged
slugged :name
end
a = Article.new :headline => "this is a great headline!", :kicker => "attention-drawing kicker"
a.save # works, slug is set
s = Station.new :name => "Great Music"
s.save # TypeError: nil is not a symbol (in sluggerize where "self.send fields" is called)
您的代码对我来说在1.9.2下工作正常:
class Foo
class << self
def slugged(fields)
method = <<-EOS
def slug_fields
#{ fields.is_a?(Array) ? fields.inspect : ":#{ fields }" }
end
EOS
class_eval method
end
end
end
Foo.slugged :a
p Foo.new.slug_fields
#=> :a
Foo.slugged [:a,:b]
p Foo.new.slug_fields
#=> [:a, :b]
p RUBY_DESCRIPTION
#=> "ruby 1.9.2p180 (2011-02-18) [i386-mingw32]"
您能否提供一个适合您的完整,可运行的独立测试用例?
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