James Byrne wrote:
Is this a semantic confusion on my part? Should I consider that what I
do with x.exists? is tell the object to answer a question?
Consider...
if x.exists?
x.important_method()
else
# nothing!
end
Now lets upgrade the variable x. Sometimes it points to a thing that exists, and
sometimes it points to a stub object whose only job is to return 'false' from
exists?, and do nothing inside important_method():
if x.exists?
x.important_method()
else
x.important_method()
end
Now you can take out the if!
x.important_method()
We are no longer asking x if it exists. We are telling it what to do, and
letting it decide how to do it. That is the heart of OO programming.
(There is still an 'if', somewhere - the one that populates x. But - hopefully -
it's only in one place.)
--
Phlip
http://www.zeroplayer.com/
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