Question

我正在做一些case.. when..，我发现了这种行为。

case vehicle.class
when Bike
  puts "This is a Bike"
when Car
  puts "This is a car"
else
  puts "May be it's an UFO."
  raise "ALIENS"
end

我发现，即使变量vehicle是Bike的一个实例，它也没有通过产生输出“这是一辆自行车”。相反，它引发了一个例外。

我觉得这很奇怪，因为以下代码会输出It's a string。

case "FooBar"
when String
  puts "It's a string"
else
  puts "It's not a string"
end

我尝试了better_errors的实时shell，发现了以下内容。

>> vehicle.class
=> Vehicle(id:integer, name: string, … , updated_at: datetime)
>> Vehicle
=> Vehicle(id:integer, name: string, … , updated_at: date time)

>> vehicle.class == Vehicle
=> true
>> vehicle.class === Vehicle
=> false

或者这与RACK_ENV？

有关

Answer 1

如果vehicle是Bike的实例，则Bike === vehicle为true。另一方面，vehicle.class为Bike，因此Bike === vehicle.class与Bike === Bike相同，因为false的类Bike是Class，不是Bike。

取消class。

case vehicle
when Bike
  puts "This is a Bike"
when Car
  puts "This is a car"
else
  puts "May be it's an UFO."
  raise "ALIENS"
end

Answer 2

===在后台的case语句中使用，并测试右侧是否是左侧类的成员。（请注意，结果不是可交换的。）

>> Fixnum === 2
=> true
>> class Vehicle; end
=> nil
>> class Truck < Vehicle; end
=> nil
>> Truck === Truck.new
=> true
>> Vehicle === Truck.new
=> true
>> Truck.new === Truck
=> false

Ruby和Rails，ActiveRecord类比较的==和===之间的区别是什么？

2 个答案: