CODEWITHSUNDEEP
ruby
Dean Winchester
Dean Winchester

Reputation: 659

How does Object#respond_to? work?

See this class definition:

class T
  def respond_to?(name)
    name.to_s == 't' || super
  end

  def t; p 't'; end
  def t2; p 't2'; end
end

When I call 

T.new.respond_to? :t2

It seems that it would return false, because either it equals to 't', nor does it respond to T's super class, which is Object. However, it returns true. So can anybody explain how this works?

Update: I realize what I thought before was wrong.

class P
  def t; self.class; end
end

class C < P
  def t
    p self.class
    p super
  end
end

When I call C.new.t

I'd expect the result to be:

C
P

However, I got:

C
C

So return to the respond_to? issue, when I call super, it runs Object#respond_to?, but still in the context/scope of C, so it returns true.

Upvotes: 1

Views: 146

Answers (2)

Frederick Cheung
Frederick Cheung

Reputation: 84114

super doesn't mean "forget you're an instance of T", it means call your superclass' implementation of respond_to?

That implementation isn't hard coded to check Object's method, it's a general implementation that goes over the object's ancestors checking for the existance of the method.

Upvotes: 1

xdazz
xdazz

Reputation: 160843

The super does not mean check whether it respond to T's super class, but just mean using the respond_to method extended from the T's super class.

Because T has the instance method t2, so it will return true.

Upvotes: 2

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