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I have three objects that are all the same class. One was created via Item.new and the other two were pulled from the database (Mongoid). I'm passing one/any of these objects to another method and checking the type in that method via is_a?:
def initialize (item, attrs = nil, options = nil)
super(attrs, options)
raise 'invalid item object' unless item.is_a?(Item)
Well, this raise is getting hit. So I check the class, is_a and instance_of in rails console. I'm getting conflicting results. Why would they have the same class but only one of them be an instance_of that class?
>> i0.is_a? Item
=> false
>> i1.is_a? Item
=> false
>> i2.is_a? Item
=> true
>> i0.class
=> Item
>> i1.class
=> Item
>> i2.class
=> Item
>> i0.instance_of?(Item)
=> false
>> i1.instance_of?(Item)
=> false
>> i2.instance_of?(Item)
=> true
Is there a better way to do this type checking of my inputs? Why would three things that are the same class not all be instances of that class?
414
The is_a? method will return a true value if an object is a of the type given as a parameter OR if it inherits from the type given as a parameter. So in effect, you can use it to ask "is there going to be a method from a class which I can run on this object".
In Ruby, Integers are object of class Fixnum(32 or 64 bits) or Bignum(used for bigger numbers). Floating-point numbers: Numbers with decimal points are usually called floats, e.g., 1.2, 10.0. The floating-point numbers are object of class Float.
I don't know Mongoid, but usually, in a DB access library, you don't get the actual object out of the database but rather a proxy object that acts as a stand-in for the object stored in the DB. Since Ruby lacks the features to implement a perfect transparent proxy, you will sometimes see odd results, especially when using reflection or around object identity.
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