What is the difference between
case item.class when MyClass # do something here when Array # do something different here when String # do a third thing end and
case item.class when MyClass.class # do something here when Array.class # do something different here when String.class # do a third thing end For some reason, the first one of these works sometimes and the second doesn't, and other times, the second one works and the first one doesn't. Why? Which one is the "proper" way to do it?
You must use:
case item when MyClass ... I had the same problem: How to catch Errno::ECONNRESET class in "case when"?
Yeah, Nakilon is correct, you must know how the threequal === operator works on the object given in the when clause. In Ruby
case item when MyClass ... when Array ... when String ... is really
if MyClass === item ... elsif Array === item ... elsif String === item ... Understand that case is calling a threequal method (MyClass.===(item) for example), and that method can be defined to do whatever you want, and then you can use the case statement with precisionw
arr = [] then I noticed that if Array === arr will evaluate to true but if arr === Array will evaluate to false. Can someone please help explain?
You can use:
case item.class.to_s when 'MyClass' ...when the following twist is not possible:
case item when MyClass The reason for this is that case uses ===, and the relationship the === operator describes is not commutative. For example, 5 is an Integer, but is Integer a 5? This is how you should think of case/when.
In Ruby, a class name is a constant that refers to an object of type Class that describes a particular class. That means that saying MyClass in Ruby is equivalent to saying MyClass.class in Java.
obj.class is an object of type Class describing the class of obj. If obj.class is MyClass, then obj was created using MyClass.new (roughly speaking). MyClass is an object of type Class that describes any object created using MyClass.new.
MyClass.class is the class of the MyClass object (it's the class of the object of type Class that describes any object created using MyClass.new). In other words, MyClass.class == Class.
It depends on the nature of your item variable. If it is an instance of an object, e.g.
t = 5 then
t.class == Fixnum but if it is a class in itself e.g
t = Array then it will be a Class object, so
t.class == Class EDIT: please refer to How to catch Errno::ECONNRESET class in "case when"? as stated by Nakilon since my answer could be wrong.
MyClass === objuses the Module#=== method to check ifobjis an instance ofMyClass.