所以我有这种情况,我想以编程方式定义一堆类.我在下面使用的方法工作正常,除了我从这里继承的第三方类不喜欢这个类是匿名定义的事实(基本上,它没有它需要的信息,即在我有机会将匿名类设置为常量之前,在’继承’钩子中的类名.
['one','two','three'].each do |model|
cls = Class.new(ThirdPartyClass) do
define_method :model do
model
end
end
ThirdPartyClass.const_set(model.capitalize,cls)
end
我可以简单地使用eval并将类定义为：
['one','three'].each do |model|
eval "class ThirdPartyClass::#{model.capitalize} < ThirdPartyClass; ...; end"
end
但我不喜欢它,因为那时它是凌乱的字符串插值.基于块的方法似乎“更好”,从美学角度讲.
有没有什么方法可以使用基于块的语法非匿名地定义该类(即从头开始使用名称),或者我注定要留在eval凌乱的字符串输入的土地上？
解决方法
创建类时,将调用Class#inherited callback.在实例化匿名类时,这将始终在将类分配给常量之前,为其指定名称.我看不出有什么方法可以解决这个问题.您可以通过使用eval创建一个空类来最小化字符串eval中的代码量,该类使用在继承之前使名称可见的特殊类语法,然后以块形式跟进class_eval来定义方法.
class Super
def self.inherited(child)
puts "#{self.name} inherited by #{child.inspect} named '#{child.name}'"
end
end
# Your way,inherited can't see name
['one','three'].each do |model|
klassname = model.capitalize
klass = Class.new(Super) do
puts "defining #{model} inheriting from Super"
define_method :model do
model
end
end
Super.const_set(klassname,klass)
end
# this way inherited sees name because we use special class definition Syntax in minimal string eval
['four','five','six'].each do |model|
klassname = model.capitalize
eval %Q{
class Super::#{klassname} < Super
puts %Q[defining Super::#{klassname} inheriting from Super]
end
}
Super.const_get(klassname).class_eval do
puts "defining methods for Super::#{klassname} inheriting from Super"
define_method :model do
model
end
end
end
# produces:
Super inherited by #<Class:0x0000010084c988> named ''
defining one inheriting from Super
Super inherited by #<Class:0x0000010084c640> named ''
defining two inheriting from Super
Super inherited by #<Class:0x0000010084c320> named ''
defining three inheriting from Super
Super inherited by Super::Four named 'Super::Four'
defining Super::Four inheriting from Super
defining methods for Super::Four inheriting from Super
Super inherited by Super::Five named 'Super::Five'
defining Super::Five inheriting from Super
defining methods for Super::Five inheriting from Super
Super inherited by Super::Six named 'Super::Six'
defining Super::Six inheriting from Super
defining methods for Super::Six inheriting from Super