[ruby-talk:8831] Re: abstract classes

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Hi,

I was mainly thinking about abstract in the java sense:
non-instatiable classes with methods that are to be 
implemented in subclasses:

something like:

class Employee
  def-abstract-method work;
  ... other ...
end

class Worker << Employee
  def work
    # do the worker job
  end
  ... other ...
end

class << Secretary
  # work not impemented
  ... other
end

1. Worker.new(...).work    #-> OK
2. Secretary.new(...).work #-> Error: abstract mathod "work" not implemented
3. Employee.new(...)       #-> Error: cannot instatiate abstract class

I know that "work" could be implemented in Employee with an exception
thrown.
This would solve case 2, but still an Employee could be instantiated (3.),
which
conceptually is not a good thing.

Is the solution to declare Emplyee as a module?

maurice

# 
# >is there any way to declare abstract classes/methods in ruby?
# 
# It depends on what you mean by abstract classes. 
# You can prevent people from invoking a new 
# operator by making it a protected method.
# 
# Can you give an example of what you would like to 
# accomplish?
# 
# Kevin
# 

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<TITLE>RE: [ruby-talk:8754] Re: abstract  classes</TITLE>
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<P><FONT SIZE Hi,</FONT>
</P>

<P><FONT SIZE I was mainly thinking about abstract in the java sense:</FONT>
<BR><FONT SIZE non-instatiable classes with methods that are to be </FONT>
<BR><FONT SIZE implemented in subclasses:</FONT>
</P>

<P><FONT SIZE something like:</FONT>
</P>

<P><FONT SIZE class Employee</FONT>
<BR><FONT SIZE &nbsp; def-abstract-method work;</FONT>
<BR><FONT SIZE &nbsp; ... other ...</FONT>
<BR><FONT SIZE end</FONT>
</P>

<P><FONT SIZE class Worker &lt;&lt; Employee</FONT>
<BR><FONT SIZE &nbsp; def work</FONT>
<BR><FONT SIZE &nbsp;&nbsp;&nbsp; # do the worker job</FONT>
<BR><FONT SIZE &nbsp; end</FONT>
<BR><FONT SIZE &nbsp; ... other ...</FONT>
<BR><FONT SIZE end</FONT>
</P>

<P><FONT SIZE class &lt;&lt; Secretary</FONT>
<BR><FONT SIZE &nbsp; # work not impemented</FONT>
<BR><FONT SIZE &nbsp; ... other</FONT>
<BR><FONT SIZE end</FONT>
</P>

<P><FONT SIZE 1. Worker.new(...).work&nbsp;&nbsp;&nbsp; #-&gt; OK</FONT>
<BR><FONT SIZE 2. Secretary.new(...).work #-&gt; Error: abstract mathod &quot;work&quot; not implemented</FONT>
<BR><FONT SIZE 3. Employee.new(...)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; #-&gt; Error: cannot instatiate abstract class</FONT>
</P>

<P><FONT SIZE I know that &quot;work&quot; could be implemented in Employee with an exception thrown.</FONT>
<BR><FONT SIZE This would solve case 2, but still an Employee could be instantiated (3.), which</FONT>
<BR><FONT SIZE conceptually is not a good thing.</FONT>
</P>

<P><FONT SIZE Is the solution to declare Emplyee as a module?</FONT>
</P>

<P><FONT SIZE maurice</FONT>
</P>

<P><FONT SIZE # </FONT>
<BR><FONT SIZE # &gt;is there any way to declare abstract classes/methods in ruby?</FONT>
<BR><FONT SIZE # </FONT>
<BR><FONT SIZE # It depends on what you mean by abstract classes. </FONT>
<BR><FONT SIZE # You can prevent people from invoking a new </FONT>
<BR><FONT SIZE # operator by making it a protected method.</FONT>
<BR><FONT SIZE # </FONT>
<BR><FONT SIZE # Can you give an example of what you would like to </FONT>
<BR><FONT SIZE # accomplish?</FONT>
<BR><FONT SIZE # </FONT>
<BR><FONT SIZE # Kevin</FONT>
<BR><FONT SIZE # </FONT>
</P>

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