From: "Jan E." <lists@...>
Date: 2012-08-25T06:20:52+09:00
Subject: Re: learning by doing part 2 - tc game

Hi,

The "defined?" operator is simply wrong in this case. It checks *the 
current scope* for variables, methods etc.

For example:

x = 0
C = 15
puts defined? x  # this outputs "local-variable"
puts defined? C  # this outputs "constant"
puts defined? a  # this outputs nothing (because the result is nil)

You want something completely different, namely check if an object has a 
specific method. That's what Object#respond_to? is for:

def effect_output(card)
  if card.respond_to? :attack
    puts "#{card.name.capitalize} hits with #{card.attack}."
  elsif card.respond_to? :heal
    puts "#{card.name.capitalize} heals for #{card.heal}."
  end
end

This will call "attack" and "heal" only if the card object does actually 
have those methods.

What should have made you suspicious is that you never had to specify 
any object. How is Ruby then supposed to know that you want to look into 
the card object?

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