[RUBY] About singular methods


I have summarized Ruby's singular methods and singular classes as a memorandum.

Singular method

In Ruby, you can define a method that is unique to an object directly, and that method is called a singular method.

class Hoge

obj = Hoge.new

def obj.method1
  p 'Singular method'


# => "Singular method"

You should be able to confirm that method1 was called in this way. So what are the consequences of another object?

obj2 = Hoge.new

# => undefined method `method1'

I got an error like this. You can see that it is a method unique to ʻobj` even in the same class.

The identity of the singular method

You can see that you can't call a method if it's an object that doesn't define a singular method even in the same class. To be on the safe side, let's use singleton_methods to make sure that the Hoge class doesn't really have any singular classes.

class Hoge

obj = Hoge.new

def obj.method1
  p 'Singular method'

p Hoge.singleton_methods
p obj.singleton_methods

# => []
# => [:method1]

However, if a method belongs to a class, you may be starting to wonder which class the singular method belongs to. As a result of investigation, it seems that there is a ** singular class ** and the singular method belongs to that class.

Singular class

To be honest, I only understand that singular classes define singular methods. Let's check the contents using ʻancestors`.

p obj.singleton_class.ancestors

# => [#<Class:#<Hoge:0x00007fca5c866ab8>>, Hoge, Object, Kernel, BasicObject]

As you can see, the superclass of the singular class is like your own class. The method search seems to be in the order of singular class → own class → superclass ....

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