Inheritance not working as expected

Ruby
1

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.

2

On 3/29/07, KJF [email protected] wrote:

                    'x'=>x,

                    'fontMode'=>fontMode,

puts stc.getAttributes

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 C.
concentrationstudios.com
brynmawrcs.com

3

On Mar 29, 7:35 am, “KJF” [email protected] wrote:
…

                    'w'=>h
    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

4

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().

5

On Mar 29, 1:04 pm, “Chris C.” [email protected] wrote:

    attr :attributes, true
    def getAttributes
            @attributes = {
    end

I am expecting the attributes from the super class to be included as
@@desc = ‘STATIC_TEXT_CONTROL’
concentrationstudios.com
brynmawrcs.com

Thanks for the help guys, makes sense now.