# Can't change the value of self - II
**URL:** https://rubytalk.org/t/cant-change-the-value-of-self-ii/59596
**Category:** ruby-talk
**Created:** [11 August 2010 23:44 UTC](https://rubytalk.org/t/cant-change-the-value-of-self-ii/59596 "2010-08-11T23:44:27Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@Ralph\_Shnelvar](https://rubytalk.org/u/Ralph_Shnelvar)
#### Post date: [11 August 2010 23:44 UTC](https://rubytalk.org/t/cant-change-the-value-of-self-ii/59596/1 "2010-08-11T23:44:27Z")
I'm still not "getting it."
Consider
- - -
class DirectoryString \< String
def initialize(arg)
super arg
end
def convert\_forward\_slash\_to\_back\_slash
self.gsub(/\//, "\\")
end
def convert\_forward\_slash\_to\_back\_slash!
self.gsub!(/\//, "\\")
end
def remove\_trailing\_backslash\_if\_any
self.chomp("\\")
end
def remove\_trailing\_backslash\_if\_any!
self.chomp!("\\")
end
def append\_trailing\_backslash\_if\_needed
remove\_trailing\_backslash\_if\_any + "\\"
end
def append\_trailing\_backslash\_if\_needed!
# ??? What do I do here ??? … The following is illegal
self = "Help!"
end
end
- - -
The only thing I can think of is converting from the standard IS\_A (Inheritance) to a HAS\_A (create a member variable).
If I do the latter, above, I will have to create a ton of simple "forwarding" messages.
What's the Ruby way of doing this sort of thing?
---
### Author:  [@jeremy\_Ruten](https://rubytalk.org/u/jeremy_Ruten)
#### Post date: [11 August 2010 23:52 UTC](https://rubytalk.org/t/cant-change-the-value-of-self-ii/59596/2 "2010-08-11T23:52:57Z")
You can use the #replace method to do that sort of thing:
self.replace "Help! Oh, well, I'm saved!"
This method is defined in classes String, Hash, Array, and Set, and
works the same way in each one.
jeremy
> **···**
>
> On Wed, Aug 11, 2010 at 5:44 PM, Ralph Shnelvar \ wrote:
>
> > I'm still not "getting it."
> >
> > Consider
> >
> > - - -
> > class DirectoryString \< String
> > def initialize(arg)
> > super arg
> > end
> >
> > def convert\_forward\_slash\_to\_back\_slash
> > self.gsub(/\//, "\\")
> > end
> >
> > def convert\_forward\_slash\_to\_back\_slash!
> > self.gsub!(/\//, "\\")
> > end
> >
> > def remove\_trailing\_backslash\_if\_any
> > self.chomp("\\")
> > end
> >
> > def remove\_trailing\_backslash\_if\_any!
> > self.chomp!("\\")
> > end
> >
> > def append\_trailing\_backslash\_if\_needed
> > remove\_trailing\_backslash\_if\_any + "\\"
> > end
> >
> > def append\_trailing\_backslash\_if\_needed!
> > # ??? What do I do here ??? ... The following is illegal
> > self = "Help!"
> > end
> > end
> >
> > - - -
> >
> > The only thing I can think of is converting from the standard IS\_A (Inheritance) to a HAS\_A (create a member variable).
> >
> > If I do the latter, above, I will have to create a ton of simple "forwarding" messages.
> >
> > What's the Ruby way of doing this sort of thing?
---
### Author:  [@Ralph\_Shnelvar](https://rubytalk.org/u/Ralph_Shnelvar)
#### Post date: [12 August 2010 00:12 UTC](https://rubytalk.org/t/cant-change-the-value-of-self-ii/59596/3 "2010-08-12T00:12:44Z")
Wednesday, August 11, 2010, 5:52:57 PM, you wrote:
> You can use the #replace method to do that sort of thing:
> self.replace "Help! Oh, well, I'm saved!"
> This method is defined in classes String, Hash, Array, and Set, and
> works the same way in each one.
> jeremy
jeremy,
That's great and solves my particular problem.
But what if the class being derived from does not have a replace method?
Ralph
---
### Author:  [@David\_A\_Black1](https://rubytalk.org/u/David_A_Black1)
#### Post date: [12 August 2010 00:29 UTC](https://rubytalk.org/t/cant-change-the-value-of-self-ii/59596/4 "2010-08-12T00:29:03Z")
If the object has state that can be modified, then there will be (by
definition) ways to modify that state. If it doesn't, then there won't
be, and the class in question is probably a bad starting point if you
want to create objects with state that can be modified.
That's one of the advantages of using proxy objects and delegators: you
gain an extra axis along which you can make decisions about things like
object state. Even though you can't change (say) a Fixnum, you can
create objects with integer attributes that \*can\* be changed.
David
> **···**
>
> On Thu, 12 Aug 2010, Ralph Shnelvar wrote:
>
> > Wednesday, August 11, 2010, 5:52:57 PM, you wrote:
> >
> > \> You can use the #replace method to do that sort of thing:
> >
> > \> self.replace "Help! Oh, well, I'm saved!"
> >
> > \> This method is defined in classes String, Hash, Array, and Set, and
> > \> works the same way in each one.
> >
> > \> jeremy
> >
> > jeremy,
> >
> > That's great and solves my particular problem.
> >
> > But what if the class being derived from does not have a replace method?
>
> --
> David A. Black, Senior Developer, Cyrus Innovation Inc.
>
> The Ruby training with Black/Brown/McAnally
> Compleat Philadelphia, PA, October 1-2, 2010
> Rubyist [http://www.compleatrubyist.com](http://www.compleatrubyist.com)
---
### Author:  [@Ralph\_Shnelvar](https://rubytalk.org/u/Ralph_Shnelvar)
#### Post date: [12 August 2010 00:38 UTC](https://rubytalk.org/t/cant-change-the-value-of-self-ii/59596/5 "2010-08-12T00:38:10Z")
David,
> > That's great and solves my particular problem.
> > But what if the class being derived from does not have a replace method?
> If the object has state that can be modified, then there will be (by
> definition) ways to modify that state. If it doesn't, then there won't
> be, and the class in question is probably a bad starting point if you
> want to create objects with state that can be modified.
> That's one of the advantages of using proxy objects and delegators: you
> gain an extra axis along which you can make decisions about things like
> object state. Even though you can't change (say) a Fixnum, you can
> create objects with integer attributes that \*can\* be changed.
Could you expand on this with an example, please?
---
### Author:  [@Jesus\_Gabriel\_y\_Gala](https://rubytalk.org/u/Jesus_Gabriel_y_Gala)
#### Post date: [12 August 2010 07:21 UTC](https://rubytalk.org/t/cant-change-the-value-of-self-ii/59596/6 "2010-08-12T07:21:57Z")
irb(main):001:0\> require 'delegate'
=\> true
irb(main):002:0\> class MutableFixnum \< Delegator
irb(main):003:1\> def initialize i
irb(main):004:2\> super
irb(main):005:2\> @value = i
irb(main):006:2\> end
irb(main):007:1\> def \_\_getobj\_\_
irb(main):008:2\> @value
irb(main):009:2\> end
irb(main):014:1\> def \_\_setobj\_\_ value
irb(main):015:2\> @value = value
irb(main):016:2\> end
irb(main):017:1\> def add! x
irb(main):018:2\> \_\_setobj\_\_(\_\_getobj\_\_ + x)
irb(main):019:2\> end
irb(main):020:1\> end
=\> nil
irb(main):021:0\> a = MutableFixnum.new 1
=\> 1
irb(main):022:0\> a + 3
=\> 4
irb(main):023:0\> a.add! 3
=\> 4
irb(main):024:0\> a
=\> 4
Jesus.
> **···**
>
> On Thu, Aug 12, 2010 at 2:38 AM, Ralph Shnelvar \ wrote:
>
> > David,
> >
> > > > That's great and solves my particular problem.
> >
> > > > But what if the class being derived from does not have a replace method?
> >
> > \> If the object has state that can be modified, then there will be (by
> > \> definition) ways to modify that state. If it doesn't, then there won't
> > \> be, and the class in question is probably a bad starting point if you
> > \> want to create objects with state that can be modified.
> >
> > \> That's one of the advantages of using proxy objects and delegators: you
> > \> gain an extra axis along which you can make decisions about things like
> > \> object state. Even though you can't change (say) a Fixnum, you can
> > \> create objects with integer attributes that \*can\* be changed.
> >
> > Could you expand on this with an example, please?
---
### Author:  [@Brian\_Candler](https://rubytalk.org/u/Brian_Candler)
#### Post date: [12 August 2010 08:00 UTC](https://rubytalk.org/t/cant-change-the-value-of-self-ii/59596/7 "2010-08-12T08:00:06Z")
Ralph Shnelvar wrote:
> Could you expand on this with an example, please?
[Just to show that delegation is nothing magic, and you don't need to
use the Delegator class]
class MyCounter
def initialize(n=0)
@n = n
end
def inc!
@n += 1
end
def to\_int
@n
end
def to\_s
@n.to\_s
end
end
c = MyCounter.new
c.inc!
c.inc!
puts "c is #{c}"
Some more work is required to make c duck-type like an Integer though.
> **···**
>
> --
> Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C).