New to Ruby. Probably my terminology will be a bit off.
In the Pickaxe book (first edition) they show a clever little trick with
the SongList class, where you can use [] to pull a song from the list using
either the integer index or the name of the song.
I wanted to try something like that, but with a subclass of Array rather
than writing a wrapper around an array. I had the idea I might be able to
use super:
class TalkerArray < Array #will hold a collection of Talkers.
def [](key)
if key.kind_of?(Integer)
return super[key]
else
return self.find{|t| t.name = key} #talkers have .name property.
end
end
end
but it didn't work (*). I bet there is a simple way to make something like
this work while inheriting from Array, though. Can anyone show me?
Why the heck is it looking at the Talker object? I must not understand
what 'super' does. Anyway, I put this as a postscript because it's kind of
a side issue for me. I'm guessing I don't really need 'super', or
understanding 'super', to override [] the way I want to. So I can worry
about that some other day. Which is not to say I won't listen if someone
wants to explain, it's just not my priority of the moment. Ok, really
done typing now.
Change super[key] to super(key) or super key. Remember, [] is just another method, and like other methods, it accepts the typical form.
class A
def [](key)
puts "key: #{key}"
end
end
a = A.new
a.[](5)
Outputs:
key: 5
As matz posted, super defaults to passing the same values passed to you, while super() passes zero args.
class A
def put(a)
puts a
end
end
class B<A
def put(n)
if n == 0
super "zero"
elsif n < 0
super()
else
super
end
end
end
b = B.new
b.put 0
b.put 5
b.put -1
Outputs:
zero
5
-:11:in `put': wrong number of arguments (0 for 1) (ArgumentError)
from -:11:in `put'
from -:20
So your code was invoking the super method with key as a parameter, taking the return value, and then invoking #[](key) on that.
Devin Mullins <twifkak@comcast.net> wrote in news:42C34B5F.3050300 @comcast.net:
Change super[key] to super(key) or super key. Remember, is just
another method, and like other methods, it accepts the typical form.
... So your code was invoking the super method with key as a
parameter, taking the return value, and then invoking #(key) on
that.
Devin
It took me a little while, but I get it now. It all comes together.
Very useful example.
Thanks to both of you.
Matt
There is also a spelling error - compare these:
return self.find{|t| t.name = key} # original
return self.find{|t| t.name == key} # fake - but better
