[Melbourne-pm] Interface Classes

Scott Penrose scottp at dd.com.au
Wed Mar 15 19:17:11 PST 2006

Hey guys - a quick question on "the right way"

In OO we are taught that a Class (in Perl 5 case - Module) should  
have a purpose.
It should not be just an interface you have to plug in to.
And there should not be really a Base class - from above.

But... in Perl we don't have the Interface that Java does...

So here is my question. I have a base class - let us call it "Fred".  
Now I have a new class that inherits from the Base which must inherit  
from the Base - ie: "Fred::Example1" ISA "Fred".

Later I make a new one "Fred::Example2" - which may be ISA  
"Fred::Example1" or just a "Fred".

So now the real question - should methods in "Fred" look like this...

sub blah {
	croak "Interface not implemented"

Or should they be...

sub blah {
	... do what blah would do ...

Think of this like DBI. Some methods can definitely be defined,  
especially if they are likely to be the default method - but some  
methods MUST be implemented by the driver - so should they have one  
of the above. In DBI land this would be silly - eg: Who gets top  
billing ?

Another alternative is that it itself becomes its own form of a Mock  
object for testing. In DBI case you would my $dbh = DBI->connect();
or something.

What are thoughts on style here?


* - *  http://www.osdc.com.au - Open Source Developers Conference * - *
Scott Penrose
VP in charge of Pancakes
scottp at dd.com.au

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Microsoft is not the answer. It's the question. And the answer is no.

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