Confusion in instance method calls of super class from subclass

ruby-talk
1

I was just playing to see the instance method calls from the subclass
and used the below code of my test:

    class Animal
      def bark
        p "hukkhh"
      end
    end
    #=> nil

    class Cow < Animal
    end
    #=> nil

    Cow.public_instance_method(:bark)
    #=> #<UnboundMethod: Cow(Animal)#bark>

    class Cow
      bark
    end
    #=> NameError: undefined local variable or method `bark' for
Cow:Class
    # from (irb):11:in `<class:Cow>'
    # from (irb):10
    # from C:/Ruby193/bin/irb:12:in `<main>'

From that code I was confirmed that instance method can't be executed
without the object instance of the respective class.

But then I tried below code:

    def talk
      p "hi"
    end
    #=> nil

    Object.public_instance_method(:talk)
    #=> #<UnboundMethod: Object#talk>

    class Foo
      talk
    end
    # prints: hi
    #=> "hi"

Here the output made me confused with my first test code output.

Could anyone help me to understand the fact behind these above?

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2

Why do you think? You added #talk to Object, Foo inherits from Object, so
it works.

···

On 3/2/13 12:42 PM, "Kumar R." <lists@ruby-forum.com> wrote:

I was just playing to see the instance method calls from the subclass
and used the below code of my test:

   class Animal
     def bark
       p "hukkhh"
     end
   end
   #=> nil

   class Cow < Animal
   end
   #=> nil

   Cow.public_instance_method(:bark)
   #=> #<UnboundMethod: Cow(Animal)#bark>

   class Cow
     bark
   end
   #=> NameError: undefined local variable or method `bark' for
Cow:Class
   # from (irb):11:in `<class:Cow>'
   # from (irb):10
   # from C:/Ruby193/bin/irb:12:in `<main>'

From that code I was confirmed that instance method can't be executed
without the object instance of the respective class.

But then I tried below code:

   def talk
     p "hi"
   end
   #=> nil

   Object.public_instance_method(:talk)
   #=> #<UnboundMethod: Object#talk>

   class Foo
     talk
   end
   # prints: hi
   #=> "hi"

Here the output made me confused with my first test code output.

Could anyone help me to understand the fact behind these above?

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3

classes are instances of Class, and this is a child class of Object

so methods defined in Object class works in other classes too

···

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4

the main object is different ... everything that is defined there is
automatic defined as private method in the Object class too

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5

YOU DID NOT READ WHAT I WAS WRITTEN:

classes are instances of Class, and this is a child class of Object
so methods defined in Object class works in other classes too

its not added as a class method, but because each class is an Object,
methods are defined in the Object class are callable from EACH OTHER
OBJECT TOO, INCLUDING EACH OTHER CLASS OBJECT!

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6

D. Deryl Downey wrote in post #1099862:

Why do you think? You added #talk to Object, Foo inherits from Object,
so
it works.

Yes, you are absolutely right. But my confusion was with `Cow` class
which is a subclass of `Animal`. and the `Animal` class has the `public
instance method` `bark`. Now as `talk` method defined in the top
level,why the bare called to `bar` has been denied from the `Cow` class.
I might have some wrong conception here I am sure.

Could you clarify on that regard?

Thanks for showing your interest.

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7

Hans Mackowiak wrote in post #1099873:

the main object is different ... everything that is defined there is
automatic defined as private method in the Object class too

@Hans if you see my code above,you will find that`talk` is being added
as `public` method but not as `private` method.

One more thing is that as below:

C:\>irb --simple-prompt

def talk
      p "hi"
end

=> nil

Object.public_instance_method(:talk)

=> #<UnboundMethod: Object#talk>

Object.public_method(:talk)

=> #<Method: Class(Object)#talk>

Why `talk` has been added as `class method and instance method` as well.
Could you help me to understand the logic?

Thanks in advance. :slight_smile:

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8

Hans Mackowiak wrote in post #1099900:

YOU DID NOT READ WHAT I WAS WRITTEN:

classes are instances of Class, and this is a child class of Object
so methods defined in Object class works in other classes too

its not added as a class method, but because each class is an Object,
methods are defined in the Object class are callable from EACH OTHER
OBJECT TOO, INCLUDING EACH OTHER CLASS OBJECT!

Okay! That I saw. I mentioned that its as public method not the private
one. as you said - "the main object is different ... everything that is
defined there is automatic defined as **private** method in the Object
class too".

I understood why `talk` succeeded. MY confusion was with the `bar` call
DUDE. :slight_smile:

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9

That confusion is because you're a moron who refuses to follow any of our advice... like READING a book or even a website in order to learn the language and basic concepts around object oriented programming. As MANY have pointed out already, you have yet to learn the difference between instances and classes as well as instance methods and class methods. Once you understand that VERY SIMPLE CONCEPT that many here have pointed you at, all of these questions fall away and you have the opportunity to possibly be an asset to this community instead of a help vampire.

···

On Mar 3, 2013, at 01:39 , "Kumar R." <lists@ruby-forum.com> wrote:

I understood why `talk` succeeded. MY confusion was with the `bar` call
DUDE. :slight_smile:

10

Ryan Davis wrote in post #1099902:

I understood why `talk` succeeded. MY confusion was with the `bar` call
DUDE. :slight_smile:

all of these questions fall away and you have the

opportunity to possibly be an asset to this community instead of a help
vampire.

So you are insisting someone not to ask questions, and only to answers.
But no one ask any questions then what's the purposes of community. It's
I think to help someone who stuck. And the links and books you are
referring they itself told if any confusion ask in the community. But
community members Like Ryan you disobeyed that. First you think and tell
me to whom should I hear ?

Thanks

···

On Mar 3, 2013, at 01:39 , "Kumar R." <lists@ruby-forum.com> wrote:

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11

my guess Cow is meant to be made a class of Object first before calling it
if left unclear it is either a method or object hence your bark is lost

···

On Sun, Mar 3, 2013 at 9:06 PM, Kumar R. <lists@ruby-forum.com> wrote:

Ryan Davis wrote in post #1099902:
> On Mar 3, 2013, at 01:39 , "Kumar R." <lists@ruby-forum.com> wrote:
>
>> I understood why `talk` succeeded. MY confusion was with the `bar` call
>> DUDE. :slight_smile:
>
all of these questions fall away and you have the
> opportunity to possibly be an asset to this community instead of a help
> vampire.

So you are insisting someone not to ask questions, and only to answers.
But no one ask any questions then what's the purposes of community. It's
I think to help someone who stuck. And the links and books you are
referring they itself told if any confusion ask in the community. But
community members Like Ryan you disobeyed that. First you think and tell
me to whom should I hear ?

Thanks

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12

But you have to *try harder* reading them *first*.

You are really the most annoying poster I ever encountered in the
2 something years I'm in this list. You repeatedly insult us
and make people shout at each other and turn away form this list,
where right now YOU take up about 50% of the traffic!

Have you ever tried to write a program with more than 5 lines?
One that actually *does* something?

You try to learn the language on a theoretical level that has really
no relevance to the things you should care about as a beginner.
For example, up to now I had *never* to care about the return value
of a class or method definition. For what do you need them...?
In case you don't need them right now for a very specific purpose,
that's just wasted time you should spend better.

···

Am 03.03.2013 11:06, schrieb Kumar R.:

I think to help someone who stuck. And the links and books you are
referring they itself told if any confusion ask in the community. But

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13

unknown wrote in post #1099908:

I think to help someone who stuck. And the links and books you are
referring they itself told if any confusion ask in the community. But

But you have to *try harder* reading them *first*.

You try to learn the language on a theoretical level that has really
no relevance to the things you should care about as a beginner.
For example, up to now I had *never* to care about the return value
of a class or method definition. For what do you need them...?
In case you don't need them right now for a very specific purpose,
that's just wasted time you should spend better.

Yes, theory is first essentials rather than problem solving.

If you don't know what's the value of Sin30 then how would you solve the
equation sin 30 + cos 30 ?

Programming language works also that way. First concept and then problem
solving skills. And problem solving is not a great challenge to any one
who did it already with other languages.

To know the features of a specific language is the very essentials one.

This is very humble request to you not to make my thread dirty,so that
future reader would end up their internal patience before reaching to
ultimate information.

Don't say I underestimate others, which in turn others did with me. I
here just asked question that raised in my mind.

···

Am 03.03.2013 11:06, schrieb Kumar R.:

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14

Yes, theory is first essentials rather than problem solving.

If you don't know what's the value of Sin30 then how would you solve the
equation sin 30 + cos 30 ?

EXACTLY.
And you didn't learn what 1+1 is but are trying to understand sin.

BTW:
1. you probably meant sin(30°), and
2. sin(30°) + cos(30°) is not an equation.

To know the features of a specific language is the very essentials one.

Agreed, but you have to start with the *basic* features,
not with implementation details that have no relevance whatsoever
for 99% of the code that people write.

This is very humble request to you not to make my thread dirty,so that
future reader would end up their internal patience before reaching to
ultimate information.

You make this whole list "dirty", and many list members already have
lost their patience.

To avoid further dirt, please do not answer this post.

···

Am 03.03.2013 12:34, schrieb Kumar R.:

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15

unknown wrote in post #1099911:

Yes, theory is first essentials rather than problem solving.

If you don't know what's the value of Sin30 then how would you solve the
equation sin 30 + cos 30 ?

BTW:
1. you probably meant sin(30°), and
2. sin(30°) + cos(30°) is not an equation.

I thought you are well capable of why I used the above example. Because
`hints` is enough for smart people.

To avoid further dirt, please do not answer this post.

Yes, I should,as you again insulted me.

EXACTLY.
And you didn't learn what 1+1 is but are trying to understand sin.

You might have the perception that CAT= TIGER. Then there is no rule
that others should believe.

···

Am 03.03.2013 12:34, schrieb Kumar R.:

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16

I thought you are well capable of why I used the above example. Because
`hints` is enough for smart people.

This is only another example on how "well" you do your reading/research.
You also for example don't even care to remove typos from your posted
code examples that you had noticed yourself. That's "dirtying" a thread.

Yes, I should,as you again insulted me.

No, it's you that keeps insulting people who are trying to
give you advice on what is not worth learning at this stage.

From now on I will ignore your posts completely, even if
they should happen to contain some valid question.

···

Am 03.03.2013 13:25, schrieb Kumar R.:

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