Basic OO Class question

ruby-talk
1

Hi All

I am try to get up to speed on several things at once; namely, OO and
also Ruby. I have written a bunch or Ruby scripts to perform various
text processing tasks but I think I want to start learning something
about OO Programming. I do have the book "Programming Ruby" and it is a
great help.

My question is related to writing a class for something like a polygon.
It can be described by a few integer and string properties. So I could
do something like this snippet:

class Zone

    attr_accessor :type, :length

    def initialize(type, length)
      @type = type
      @length = length
    end

end

testZ = Zone.new("Rad", 20.1)

Here is what I don't know how to do. How do I add an array of integers
to this class? It would need to be of variable length.

Sorry for the basic question?

Kev

···

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

2

Give it an accessor and then initialize the associated instance variable to
an array.

class Zone

  attr_accessor :type, :length, :integers

  def initialize(type, length)
    @type = type
    @length = length
    @integers = Array.new
  end

end

test_z = Zone.new("Rad", 20.1)
test_z.integers # =>
test_z.integers << 1
test_z.integers # => [1]
test_z.integers << 2
test_z.integers # => [1, 2]

In terms of the integers part, you can't specify the array should contain
integers, I've named it integers to indicate that's what it is, but really
you could put anything in there.

···

On Sun, Oct 9, 2011 at 5:44 PM, Kevin E. <kellwood@gmail.com> wrote:

Hi All

I am try to get up to speed on several things at once; namely, OO and
also Ruby. I have written a bunch or Ruby scripts to perform various
text processing tasks but I think I want to start learning something
about OO Programming. I do have the book "Programming Ruby" and it is a
great help.

My question is related to writing a class for something like a polygon.
It can be described by a few integer and string properties. So I could
do something like this snippet:

class Zone

   attr_accessor :type, :length

   def initialize(type, length)
     @type = type
     @length = length
   end

end

testZ = Zone.new("Rad", 20.1)

Here is what I don't know how to do. How do I add an array of integers
to this class? It would need to be of variable length.

Sorry for the basic question?

Kev

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

3

Thanks all for replying. This helps me get started.

Robert, "type" is a variable that differentiates the zone instances so
that they can have different behaviors. "length" is a dimension of a
zone.

Kev

···

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

4

That's one of the reasons why I sometimes prefer a more robust approach

class Zone

attr_accessor :type, :length

def initialize(type, length)
   @type = type
   @length = length
   @integers = # same as Array.new
end

  def add(an_int)
    @integers << an_int.to_int
    self
  end

  def integers
    @integers.dup
  end
end

This does two things:

1. ensure that only integers are put into the array by doing conversion #to_int.

2. copies the array on access to avoid someone outside the instance to
mess with internal state.

Whether this added robustness is needed depends on the application.
You like also have to add methods for removing entries again etc.

Kevin:

Btw, what is the "type" member supposed to mean? If that should
control behavior in some way then strategy pattern (or a similar one)
would be a better solution.

http://c2.com/cgi/wiki?StrategyPattern

2nd note: if @length should represent the length of the Array you do
not need a separate member. Instead you can do

def length
  @integers.length # or .size
end

Kind regards

robert

···

On Mon, Oct 10, 2011 at 2:53 AM, Josh Cheek <josh.cheek@gmail.com> wrote:

On Sun, Oct 9, 2011 at 5:44 PM, Kevin E. <kellwood@gmail.com> wrote:

Hi All

I am try to get up to speed on several things at once; namely, OO and
also Ruby. I have written a bunch or Ruby scripts to perform various
text processing tasks but I think I want to start learning something
about OO Programming. I do have the book "Programming Ruby" and it is a
great help.

My question is related to writing a class for something like a polygon.
It can be described by a few integer and string properties. So I could
do something like this snippet:

class Zone

attr_accessor :type, :length

def initialize(type, length)
@type = type
@length = length
end

end

testZ = Zone.new("Rad", 20.1)

Here is what I don't know how to do. How do I add an array of integers
to this class? It would need to be of variable length.

Give it an accessor and then initialize the associated instance variable to
an array.

class Zone

attr_accessor :type, :length, :integers

def initialize(type, length)
@type = type
@length = length
@integers = Array.new
end

end

test_z = Zone.new("Rad", 20.1)
test_z.integers # =>
test_z.integers << 1
test_z.integers # => [1]
test_z.integers << 2
test_z.integers # => [1, 2]

In terms of the integers part, you can't specify the array should contain
integers, I've named it integers to indicate that's what it is, but really
you could put anything in there.

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

5

"type" is a variable that differentiates the zone instances so
that they can have different behaviors.

That's what making subclasses is usually used for.

For example if you need an area() function, you might make your Zone
class uninstantiatable (what in C++ would call an "abstract class",
and Java would call an "interface". (Or you could have a default Zone
shape, like say maybe a line, so its area would be a constant zero --
idealized line, zero thickness.) Then you could create subclasses
like Square, Circle, EquilateralTriangle, Hexagon, and so on, where
you'd only need to know one given dimension, which would probably be
the length of a side of a polygon, and maybe the radius of a circle.
Then you'd "override" (change the definition of) the area function, to
apply the correct formula for that shape.

For instance:

class Zone
  # let's skip most of it
  def area
    0
  end
end

class Square < Zone
  # again, let's skip most of it
  def area
    length * length
  end
end

class Circle < Zone
  # once more, let's skip most of it
  def area
    Math.PI * length * length
  end
end

So then you could have an object that you know is a Zone... but you
don't know (nor *care*!) whether it's *just* a Zone, or whether it's
some subclass like Square or Circle or whatever, you can still call
area() on it, and get back an answer. As in:

  z = CreateRandomZone
  a = z.area

"length" is a dimension of a zone.

This part makes sense though. Class instances (i.e., objects) usually
do have some attributes, properties, or whatever you want to call
them. There are things that vary according to which instance it is
(i.e., *which* Square, or *which* Circle), which become instance
attributes. Some vary according to which class (like, for the
polygonal subclasses, might be something like number_of_sides) it is,
and become class attributes (since they don't need to be stored on
each instance).

-Dave

···

On Mon, Oct 10, 2011 at 18:59, Kevin E. <kellwood@gmail.com> wrote:

--
LOOKING FOR WORK, preferably Ruby on Rails, in NoVa/DC; see main web site.
Main Web Site: davearonson.com
Programming Blog: codosaur.us
Excellence Blog: dare2xl.com

6

Interesting, I like it. I usually only dup data if I find I need it, but for
lib code it probably makes sense to be more proactive. I'm a bit ambivalent
about to_int, though, I suppose it depends on the situation.

···

On Mon, Oct 10, 2011 at 3:55 AM, Robert Klemme <shortcutter@googlemail.com>wrote:

On Mon, Oct 10, 2011 at 2:53 AM, Josh Cheek <josh.cheek@gmail.com> wrote:
> On Sun, Oct 9, 2011 at 5:44 PM, Kevin E. <kellwood@gmail.com> wrote:
>
>> Hi All
>>
>> I am try to get up to speed on several things at once; namely, OO and
>> also Ruby. I have written a bunch or Ruby scripts to perform various
>> text processing tasks but I think I want to start learning something
>> about OO Programming. I do have the book "Programming Ruby" and it is a
>> great help.
>>
>> My question is related to writing a class for something like a polygon.
>> It can be described by a few integer and string properties. So I could
>> do something like this snippet:
>>
>> class Zone
>>
>> attr_accessor :type, :length
>>
>> def initialize(type, length)
>> @type = type
>> @length = length
>> end
>>
>> end
>>
>> testZ = Zone.new("Rad", 20.1)
>>
>> Here is what I don't know how to do. How do I add an array of integers
>> to this class? It would need to be of variable length.

> Give it an accessor and then initialize the associated instance variable
to
> an array.
>
>
> class Zone
>
> attr_accessor :type, :length, :integers
>
> def initialize(type, length)
> @type = type
> @length = length
> @integers = Array.new
> end
>
> end
>
> test_z = Zone.new("Rad", 20.1)
> test_z.integers # =>
> test_z.integers << 1
> test_z.integers # => [1]
> test_z.integers << 2
> test_z.integers # => [1, 2]
>
>
> In terms of the integers part, you can't specify the array should contain
> integers, I've named it integers to indicate that's what it is, but
really
> you could put anything in there.

That's one of the reasons why I sometimes prefer a more robust approach

class Zone

attr_accessor :type, :length

def initialize(type, length)
  @type = type
  @length = length
   @integers = # same as Array.new
end

def add(an_int)
   @integers << an_int.to_int
   self
end

def integers
   @integers.dup
end
end

This does two things:

1. ensure that only integers are put into the array by doing conversion
#to_int.

2. copies the array on access to avoid someone outside the instance to
mess with internal state.

Whether this added robustness is needed depends on the application.
You like also have to add methods for removing entries again etc.