Defining struct in a class
in [Ruby]
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From: William Song on 7 Jun 2010 18:16 How can I properly define a struct in a class? If I have class Cards Card = Struct.new(:suit, :number) @cardsOnHand=[] @cardsOnHand.push(Card.new("S","5")) end This will give me an error message saying the push is not defined for NilClass. How should I fix this? -- Posted via http://www.ruby-forum.com/.
From: Rein Henrichs on 7 Jun 2010 19:03 On 2010-06-07 15:16:33 -0700, William Song said: > How can I properly define a struct in a class? > > If I have > > class Cards > Card = Struct.new(:suit, :number) > @cardsOnHand=[] > > @cardsOnHand.push(Card.new("S","5")) > end > > This will give me an error message saying the push is not defined for > NilClass. How should I fix this? The error you reported has nothing to do with your Card struct. Besides which, your code works for me as is. -- Rein Henrichs http://puppetlabs.com http://reinh.com
From: William Song on 7 Jun 2010 19:16 Rein Henrichs wrote: > On 2010-06-07 15:16:33 -0700, William Song said: > >> >> This will give me an error message saying the push is not defined for >> NilClass. How should I fix this? > > The error you reported has nothing to do with your Card struct. Besides > which, your code works for me as is. Sorry, I meant to put it into a function. I over-simplified it when posted here. class Cards Card = Struct.new(:suit, :number) @cardsOnHand=[] def a() @cardsOnHand.push(Card.new("S","5")) end end cards = Cards.new cards.a() The above code will give an error. -- Posted via http://www.ruby-forum.com/.
From: Rein Henrichs on 8 Jun 2010 00:52 On 2010-06-07 16:16:57 -0700, William Song said: > Rein Henrichs wrote: >> On 2010-06-07 15:16:33 -0700, William Song said: >> >>> >>> This will give me an error message saying the push is not defined for >>> NilClass. How should I fix this? >> >> The error you reported has nothing to do with your Card struct. Besides >> which, your code works for me as is. > > Sorry, I meant to put it into a function. I over-simplified it when > posted here. > > class Cards > Card = Struct.new(:suit, :number) > @cardsOnHand=[] > > def a() > @cardsOnHand.push(Card.new("S","5")) > end > end > > cards = Cards.new > cards.a() > > The above code will give an error. You create an instance variable, @cardsOnHand, in the class scope. That means it is an instance variable of the object Cards (the class). You then attempt to access it in the scope of an instance method, i.e. on a Cards instance. They are two different objects, two different scopes and two different variables. I would suggest reading the chapter Classes, Objects and Variables in http://ruby-doc.org/docs/ProgrammingRuby to better understand the concept of scope in Ruby and how it effects variables. Hint: you probably want to set this instance variable when you *initialize* an Cards object. I would also suggest reading http://github.com/chneukirchen/styleguide/blob/master/RUBY-STYLE to get a better grasp of common Ruby style, such as two space indention, adding spacing before and after the = in a variable assignment, using camel_case for variable and method names, and removing empty () on the ends of methods. -- Rein Henrichs http://puppetlabs.com http://reinh.com
From: Angus Hammond on 8 Jun 2010 12:59
I assume you want the first two lines of you class definition to be run every time someone creates an instance of you class. If you do you should put the into a method called initialize. That will be run automatically when new is called and should solve your problem On 08/06/10 00:16, William Song wrote: > Rein Henrichs wrote: > >> On 2010-06-07 15:16:33 -0700, William Song said: >> >> >>> This will give me an error message saying the push is not defined for >>> NilClass. How should I fix this? >>> >> The error you reported has nothing to do with your Card struct. Besides >> which, your code works for me as is. >> > Sorry, I meant to put it into a function. I over-simplified it when > posted here. > > class Cards > Card = Struct.new(:suit, :number) > @cardsOnHand=[] > > def a() > @cardsOnHand.push(Card.new("S","5")) > end > end > > cards = Cards.new > cards.a() > > The above code will give an error. > |