Problem in typical code

ruby-talk
1

Hi
In a ruby learning book I faced to below code, I don't understand what
does second method do ? and what is use of self in second method ?
please help me .
thanks

···

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2

Posting the code would help a lot. :slight_smile:

···

On Tue, Aug 9, 2011 at 7:25 PM, amir e. <aef1370@gmail.com> wrote:

Hi
In a ruby learning book I faced to below code, I don't understand what
does second method do ? and what is use of self in second method ?
please help me .
thanks

--
Phillip Gawlowski

phgaw.posterous.com | twitter.com/phgaw | gplus.to/phgaw

A method of solution is perfect if we can forsee from the start,
and even prove, that following that method we shall attain our aim.
-- Leibniz

3

EXCUSE ME !!!!!!!!!!
THIS IS THE CODE :

class Fixnum
  def seconds
    self
  end
  def minutes
    self * 60
  end
  def hours
    self * 60 * 60
  end
  def days
    self * 60 * 60 * 24
  end
end

AGAIN , EXCUSE ME!!!

···

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4

hi Amir,

  "self" can be a bit confusing at times, but you can think of it as
representing whatever class (or instance of that class) you are dealing
with...

  for example:

  here, "self" is whatever Fixnum you happen to use with the #double
method

     class Fixnum

  def double
    p self * 2
  end

     end

     3.double

     => 6

  here, "self" is whatever Array you happen to create and use with the
#double method...

     class Array

  def double
    self.each_with_index{|entry, index|
      new = entry * 2
      self[index] = new
    }
  end

     end

     foo = ["a", "b", "c"]
     foo.double
     p foo

     => ["aa", "bb", "cc"]

- j

···

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5

I was about to say the same, for luck i'm not the only (insert country
of choice) zealot around here *LOL*

just kidding

···

On 08/09/2011 07:30 PM, Phillip Gawlowski wrote:

On Tue, Aug 9, 2011 at 7:25 PM, amir e. <aef1370@gmail.com> wrote:

Hi
In a ruby learning book I faced to below code, I don't understand what
does second method do ? and what is use of self in second method ?
please help me .
thanks

Posting the code would help a lot. :slight_smile:

6

EXCUSE ME !!!!!!!!!!
THIS IS THE CODE :

No need to use caps. :slight_smile:

class Fixnum
def seconds
self
end
def minutes
self * 60
end
def hours
self * 60 * 60
end
def days
self * 60 * 60 * 24
end
end

Explanation of the code:

If you type this into irb, and write something like "2.days", the
Fixnum 2 (Fixnums are a bit of a special case in Ruby, since they
don't usually get created, but just *are*) gets multiplied by seconds,
minutes, then hours. This happens because "self" is a keyword in Ruby,
which means "I want to do this to myself".

A made up example:

class Car
  def turn_key
     self.motor = "on"
  end

  def motor=(state) # A manually created 'setter method'
    @motor = state # "@motor" is an 'instance variable', meaning it is
valid only within a single Car object.
  end
end

···

On Tue, Aug 9, 2011 at 8:38 PM, amir e. <aef1370@gmail.com> wrote:

--
Phillip Gawlowski

phgaw.posterous.com | twitter.com/phgaw | gplus.to/phgaw

A method of solution is perfect if we can forsee from the start,
and even prove, that following that method we shall attain our aim.
-- Leibniz

7

I think the best way to explain it is this:

In ruby, text you type is converted into representations of tokens representing objects and methods.

The simplest way to think about it at first is to construct a model in your mind where there are a lot of objects floating around.

When you type this into ruby, you're instructing it to execute the method named "to_s" that is stored in the Fixnum class object, and to execute it on the Fixnum instance object 45:

45.to_s

What that does is create a new string object representing that Fixnum and return it to you. (ie it "falls out the end")

This is called method calling, or messaging. You're sending the object 45 the message "to_s" and it returns the result of "45".

Now, because everything is an object in the way we think about ruby, and evade ruby is quite flexible, you can do some clever things.

You can obviously create your own class objects and then create your own instance objects of these classes, but the really clever thing we're seeing here is that you can re-define the methods inside a class object once it has already been defined. You can add, or modify methods "on the fly" so to speak.

This is what's happening with your code. You're ripping open the Fixnum class object - the one that ruby uses to represents fixed numbers... That is, integers that are fairly small... And you're adding some methods. All the existing functionality will remain unless you choose a method name that is already in use and that will obviously replace an existing method if you do that.

It's important to think in your kind about context. When you're "inside" a class definition such as this:

class Fixnum
def seconds
self
end
end

Inside the class...end context, self means "the object we're currently referring to". It's whichever object is the target of the method.

So here, in the case of our Fixnum 45, because seconds is an instance object
method, it means the number 45 itself. So sending 45 the message seconds will return 45 itself.

If I were writing that code, I would probably have written it like this:

class Fixnum
def seconds
   self
end
def minutes
   self * 60.seconds
end
def hours
   self * 60.minutes
end
def days
   self * 24.hours
end
end

Experimentation is a very powerful tool in learning. Use IRB a lot and do a lot of micro experiments, or "tests" :wink:

Julian

Blog: http://random8.zenunit.com/
Twitter: http://twitter.com/random8r
Learn: http://sensei.zenunit.com/
New video up now at http://sensei.zenunit.com/
real fastcgi rails deploy process! Check it out now!

···

On 10/08/2011, at 4:38 AM, "amir e." <aef1370@gmail.com> wrote:

EXCUSE ME !!!!!!!!!!
THIS IS THE CODE :

class Fixnum
def seconds
   self
end
def minutes
   self * 60
end
def hours
   self * 60 * 60
end
def days
   self * 60 * 60 * 24
end
end

AGAIN , EXCUSE ME!!!

--
Posted via http://www.ruby-forum.com/\.

8

I forgot to say once you have this class redefined you can then write interesting things like this:

130.seconds / 1.minutes

And ruby will tell you 2. Clever, no?

Blog: http://random8.zenunit.com/
Twitter: http://twitter.com/random8r
Learn: http://sensei.zenunit.com/
New video up now at http://sensei.zenunit.com/
real fastcgi rails deploy process! Check it out now!

···

On 10/08/2011, at 10:25 AM, Julian Leviston <julian@coretech.net.au> wrote:

I think the best way to explain it is this:

In ruby, text you type is converted into representations of tokens representing objects and methods.

The simplest way to think about it at first is to construct a model in your mind where there are a lot of objects floating around.

When you type this into ruby, you're instructing it to execute the method named "to_s" that is stored in the Fixnum class object, and to execute it on the Fixnum instance object 45:

45.to_s

What that does is create a new string object representing that Fixnum and return it to you. (ie it "falls out the end")

This is called method calling, or messaging. You're sending the object 45 the message "to_s" and it returns the result of "45".

Now, because everything is an object in the way we think about ruby, and evade ruby is quite flexible, you can do some clever things.

You can obviously create your own class objects and then create your own instance objects of these classes, but the really clever thing we're seeing here is that you can re-define the methods inside a class object once it has already been defined. You can add, or modify methods "on the fly" so to speak.

This is what's happening with your code. You're ripping open the Fixnum class object - the one that ruby uses to represents fixed numbers... That is, integers that are fairly small... And you're adding some methods. All the existing functionality will remain unless you choose a method name that is already in use and that will obviously replace an existing method if you do that.

It's important to think in your kind about context. When you're "inside" a class definition such as this:

class Fixnum
def seconds
self
end
end

Inside the class...end context, self means "the object we're currently referring to". It's whichever object is the target of the method.

So here, in the case of our Fixnum 45, because seconds is an instance object
method, it means the number 45 itself. So sending 45 the message seconds will return 45 itself.

If I were writing that code, I would probably have written it like this:

class Fixnum
def seconds
  self
end
def minutes
  self * 60.seconds
end
def hours
  self * 60.minutes
end
def days
  self * 24.hours
end
end

Experimentation is a very powerful tool in learning. Use IRB a lot and do a lot of micro experiments, or "tests" :wink:

Julian

Blog: http://random8.zenunit.com/
Twitter: http://twitter.com/random8r
Learn: http://sensei.zenunit.com/
New video up now at http://sensei.zenunit.com/
real fastcgi rails deploy process! Check it out now!

On 10/08/2011, at 4:38 AM, "amir e." <aef1370@gmail.com> wrote:

EXCUSE ME !!!!!!!!!!
THIS IS THE CODE :

class Fixnum
def seconds
  self
end
def minutes
  self * 60
end
def hours
  self * 60 * 60
end
def days
  self * 60 * 60 * 24
end
end

AGAIN , EXCUSE ME!!!

--
Posted via http://www.ruby-forum.com/\.