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comp.lang.ruby

Inheritance not working as expected

KJF

3/29/2007 11:35:00 AM

I am trying to build up some classes using inheritance but I'm not
getting the expected results

Here are my classes and test data

class Control
attr :attributes, true

def initialize(x, y, w, h)
@attributes = {
'x'=>x,
'y'=>y,
'h'=>w,
'w'=>h
}
end

def getAttributes
return @attributes
end
end

class StaticTextControl < Control

def initialize(x, y, w, h, xBorder, yBorder, fontSize, fontMode,
phrase)
super(x, y, w, h)
@@desc = 'STATIC_TEXT_CONTROL'
@attributes = {
'xBorder'=>xBorder,
'yBorder'=>yBorder,
'fontSize'=>fontSize,
'fontMode'=>fontMode,
'phrase'=>phrase
}
end

def getAttributes
return @attributes.merge(super)
end
end

stc = StaticTextControl.new(1,2,3,4,5,6,7,8,9)
puts stc.getAttributes


When I run the script I get this:
returning attributes {"phrase"=>9, "xBorder"=>5, "fontSize"=>7,
"yBorder"=>6, "fontMode"=>8}
phrase9xBorder5yBorder6fontSize7fontMode8

I am expecting the attributes from the super class to be included as
well.
Can anyone tell me what I'm doing wrong?

Thanks.
4 Answers

Chris Hulan

3/29/2007 12:02:00 PM

0

On Mar 29, 7:35 am, "KJF" <Kevin.Fag...@gmail.com> wrote:
....
> Here are my classes and test data
>
> class Control
> attr :attributes, true
>
> def initialize(x, y, w, h)
> @attributes = {
> 'x'=>x,
> 'y'=>y,
> 'h'=>w,
> 'w'=>h
> }
> end
>
> def getAttributes
> return @attributes
> end
> end
>
> class StaticTextControl < Control
>
> def initialize(x, y, w, h, xBorder, yBorder, fontSize, fontMode,
> phrase)
> super(x, y, w, h)
> @@desc = 'STATIC_TEXT_CONTROL'
> @attributes = {
> 'xBorder'=>xBorder,
> 'yBorder'=>yBorder,
> 'fontSize'=>fontSize,
> 'fontMode'=>fontMode,
> 'phrase'=>phrase
> }
....
@attributes is an instance attribute, so right here you change it,
loosing the x,y,w,h values.

you should use merge here, and then there is no need to re-implement
getAttributes as the superclass method will work as expected

Cheers
Chris

Chris Carter

3/29/2007 12:04:00 PM

0

On 3/29/07, KJF <Kevin.Fagan1@gmail.com> wrote:
> I am trying to build up some classes using inheritance but I'm not
> getting the expected results
>
> Here are my classes and test data
>
> class Control
> attr :attributes, true
>
> def initialize(x, y, w, h)
> @attributes = {
> 'x'=>x,
> 'y'=>y,
> 'h'=>w,
> 'w'=>h
> }
> end
>
> def getAttributes
> return @attributes
> end
> end
>
> class StaticTextControl < Control
>
> def initialize(x, y, w, h, xBorder, yBorder, fontSize, fontMode,
> phrase)
> super(x, y, w, h)
> @@desc = 'STATIC_TEXT_CONTROL'
> @attributes = {
> 'xBorder'=>xBorder,
> 'yBorder'=>yBorder,
> 'fontSize'=>fontSize,
> 'fontMode'=>fontMode,
> 'phrase'=>phrase
> }
> end
>
> def getAttributes
> return @attributes.merge(super)
> end
> end
>
> stc = StaticTextControl.new(1,2,3,4,5,6,7,8,9)
> puts stc.getAttributes
>
>
> When I run the script I get this:
> returning attributes {"phrase"=>9, "xBorder"=>5, "fontSize"=>7,
> "yBorder"=>6, "fontMode"=>8}
> phrase9xBorder5yBorder6fontSize7fontMode8
>
> I am expecting the attributes from the super class to be included as
> well.
> Can anyone tell me what I'm doing wrong?
>
> Thanks.
>
>
>

You call super, which assigns the @attributes hash, then you just
reassign it. In the subclass you need to add to the hash not
overwrite it.

> super(x, y, w, h)
> @@desc = 'STATIC_TEXT_CONTROL'
@attributes.merge( {
'xBorder'=>xBorder,
'yBorder'=>yBorder,
'fontSize'=>fontSize,
'fontMode'=>fontMode,
'phrase'=>phrase
})


Chris Carter
concentrationstudios.com
brynmawrcs.com

KJF

3/29/2007 12:44:00 PM

0

On Mar 29, 1:04 pm, "Chris Carter" <cdcar...@gmail.com> wrote:
> On 3/29/07, KJF <Kevin.Fag...@gmail.com> wrote:
>
>
>
> > I am trying to build up some classes using inheritance but I'm not
> > getting the expected results
>
> > Here are my classes and test data
>
> > class Control
> > attr :attributes, true
>
> > def initialize(x, y, w, h)
> > @attributes = {
> > 'x'=>x,
> > 'y'=>y,
> > 'h'=>w,
> > 'w'=>h
> > }
> > end
>
> > def getAttributes
> > return @attributes
> > end
> > end
>
> > class StaticTextControl < Control
>
> > def initialize(x, y, w, h, xBorder, yBorder, fontSize, fontMode,
> > phrase)
> > super(x, y, w, h)
> > @@desc = 'STATIC_TEXT_CONTROL'
> > @attributes = {
> > 'xBorder'=>xBorder,
> > 'yBorder'=>yBorder,
> > 'fontSize'=>fontSize,
> > 'fontMode'=>fontMode,
> > 'phrase'=>phrase
> > }
> > end
>
> > def getAttributes
> > return @attributes.merge(super)
> > end
> > end
>
> > stc = StaticTextControl.new(1,2,3,4,5,6,7,8,9)
> > puts stc.getAttributes
>
> > When I run the script I get this:
> > returning attributes {"phrase"=>9, "xBorder"=>5, "fontSize"=>7,
> > "yBorder"=>6, "fontMode"=>8}
> > phrase9xBorder5yBorder6fontSize7fontMode8
>
> > I am expecting the attributes from the super class to be included as
> > well.
> > Can anyone tell me what I'm doing wrong?
>
> > Thanks.
>
> You call super, which assigns the @attributes hash, then you just
> reassign it. In the subclass you need to add to the hash not
> overwrite it.
>
> > super(x, y, w, h)
> > @@desc = 'STATIC_TEXT_CONTROL'
>
> @attributes.merge( {
> 'xBorder'=>xBorder,
> 'yBorder'=>yBorder,
> 'fontSize'=>fontSize,
> 'fontMode'=>fontMode,
> 'phrase'=>phrase
> })
>
> Chris Carter
> concentrationstudios.com
> brynmawrcs.com

Thanks for the help guys, makes sense now.

gga

4/1/2007 6:17:00 PM

0

> Can anyone tell me what I'm doing wrong?
>
> Thanks.

Besides what others have pointed out, getAttributes is member function
that should not be used.
This is a bad practice, likely carried over from more limiting
languages such as Java, C++ or Python.

You should use:

class Control
attr_reader :attributes

def initialize(x, y, w, h)
@attributes = {
'x'=>x,
'y'=>y,
'h'=>w,
'w'=>h
}
end
end

a = Control.new
attrs = a.attributes

If you do require attributes() to do something special in this or
derived class, you can just redefine it.

class DerivedControl < Control
def attributes
nil
end
end

The benefit of this approach is that your interface never changes,
regardless of whether the function is a getter/setter or a true
function that performs some more complex magic.


If, on the other hand, you do require a special member function for a
different operation other than a getter/setter, you should stick to
the ruby convention of lowercase and underscores. Thus, instead of
calculateAttributes(), you'd use calculate_attributes().