例如,假设我们有一个名为Person的.net类
class Person
{
public string Firstname{get;set;}
public string Lastname{get;set;}
public Address HomeAddress{get;set;}
}
class Address
{
public string AddressLine1{get;set;}
public string City{get;set;}
public string Country{get;set;}
}
在Ruby中,我会把它写成
class Person attr_accessor :FirstName attr_accessor :LastName attr_accessor :HomeAddress end class Address attr_accessor :AddressLine1 attr_accessor :City attr_accessor :Country end
看看Ruby版本的Person类如何为访问者方法FirstName,LastName和HomeAddress指定类型？如果我要消费这个类,我可以将任何类型的Feed添加到HomeAddress中,但是我希望这个访问器方法只接受TYPE Address.
有什么建议么 ？
谢谢
解决方法
Ruby是一种动态语言,这就是为什么你不会得到编译时类型的警告/错误,就像C#这样的语言.
与您无法为变量指定类型相同,您不能指定attr_accessor的类型.
对于来自.NET的用户来说,这可能听起来很愚蠢,但在Ruby社区,人们期望您能够编写测试.如果这样做,这些类型的问题将基本消失.在Ruby on Rails中,你应该测试你的模型.如果你这样做,你不会真的有任何麻烦,意外地分配错误的地方.
如果您正在Ruby on Rails中讨论ActiveRecord,则将String分配给数据库中定义为Integer的属性将导致抛出异常.
顺便说一句,根据惯例,你不应该使用CamelCase属性,所以正确的类定义应该是
class Person attr_accessor :first_name attr_accessor :last_name attr_accessor :home_address end class Address attr_accessor :address_line1 attr_accessor :city attr_accessor :country end
一个原因是,如果您将第一个字母大写,则Ruby将定义一个常量而不是一个变量.
number = 1 # regular variable Pi = 3.14159 # constant ... changing will result in a warning,not an error
元编程黑客
顺便说一句,Ruby还具有非常庞大的元编程能力.您可以使用类型检查编写自己的attr_accessor,可以使用类似的检查
typesafe_accessor :price,Integer
有定义的东西
class Foo
# 'static',or better said 'class' method ...
def self.typesafe_accessor(name,type)
# here we dynamically define accessor methods
define_method(name) do
# unfortunately you have to add the @ here,so string interpolation comes to help
instance_variable_get("@#{name}")
end
define_method("#{name}=") do |value|
# simply check a type and raise an exception if it's not what we want
# since this type of Ruby block is a closure,we don't have to store the
# 'type' variable,it will 'remember' it's value
if value.is_a? type
instance_variable_set("@#{name}",value)
else
raise ArgumentError.new("Invalid Type")
end
end
end
# Yes we're actually calling a method here,because class definitions
# aren't different from a 'running' code. The only difference is that
# the code inside a class definition is executed in the context of the class object,# which means if we were to call 'self' here,it would return Foo
typesafe_accessor :foo,Integer
end
f = Foo.new
f.foo = 1
f.foo = "bar" # KaboOoOoOoM an exception thrown here!
或至少这些线路的东西:)这段代码工作！ Ruby允许您快速定义方法,这是attr_accessor的工作原理.
也是块几乎总是关闭,这意味着我可以做如果value.is_a？类型,而不将其作为参数.
这是非常复杂的,在这里解释这是真的,何时不是.总之,有不同类型的块
> Pro,由Proc.new创建
> lambda,它是由关键字lambda创建的
区别之一是调用lambda中的返回值只能从lambda本身返回,但是当您从Proc执行相同的操作时,块周围的整个方法将返回,这在迭代时使用.
def find(array,something)
array.each do |item|
# return will return from the whole 'find()' function
# we're also comparing 'item' to 'something',because the block passed
# to the each method is also a closure
return item if item == something
end
return nil # not necessary,but makes it more readable for explanation purposes
end
如果你是这样的东西,我建议你看看PragProg Ruby Metaprogramming screencast.