Equivalent operations on instance of Ruby class (to Java)

Question

I'm a Java and long-time C guy trying to learn Ruby. It's a humbling experience to say the least.

I have the following class.

class Node
  @@normal
  def get_normal( n )
    @@normal[ :#n ]
  end
  def add_normal( n, value )
    @@normal[ :#{n} ] = value
  end
end

...and I'm trying to use it probably in a way that only a Java guy would, but perhaps you can set me straight. (In Java I would have:

class Node
{
   private Map< String, String > normal = new HashMap< String, String >();

   public void addToNormal( String key, String value ) { this.normal.put( key, value ); }
   public String getNormal( String key )               { return this.normal.get( key ); }
}
...
Node node = new Node();
node.addToNormal( "city", "New Orleans" );
System.out.println( node.getNormal( "city" );

)

Below, I think I'm trying to get "New Orleans" out of it, but it doesn't work. (Note: On purpose I'm trying to use Ruby symbols instead of strings for the key.)

irb(main):001:0> class Node
irb(main):002:1>   @@normal
irb(main):003:1>   def add_normal( n, value )
irb(main):004:2>     @@normal[ :#{n} ] = value
irb(main):005:3*   end
irb(main):006:3>   def get_normal( n )
irb(main):007:4>     @@normal[ :#n ]
irb(main):008:5*   end
irb(main):009:5> end
irb(main):010:4> node = Node.new()
irb(main):011:4> node.add_normal( :city, "New Orleans" )
irb(main):012:4> puts node.get_normal
irb(main):013:4> puts node.get_normal()

In short, I get nothing out of this.

I would like to incorporate using Ruby symbols as keys in the hash, but the most important thing I want to learn is using a Ruby class in the way I'm using the Java class above. Or, that this is wrong-headed? If you can spare the time, please adjust my class definition and/or what I'm trying to do with it, or generally criticize. Thank you very much!

ddavison · Accepted Answer · 2013-09-09 21:34:55Z

1

Here is your ruby class,

class Node
  def initialize
    @normal = {}
  end

  def get_normal(n)
    @normal[:n]
  end

  def add_normal(n, value)
    @normal[:n] = value
  end
end

and in your irb,

node = Node.new
node.add_normal(:city, "New Orleans")
puts node.get_normal(:city)

Couple notes,

you want to use instance variables, not a class variable for something like that. Instance variables are @my_var and class variables are @@my_var

If you leave @normal = {} at the class level, it'll be nil at the time of execution, so you put in the def initialize which is the constructor for the class.

edited Sep 9, 2013 at 21:34

answered Sep 9, 2013 at 21:25

ddavison

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4 Comments

Russ Bateman Over a year ago

This does indeed work and give me something to play with. The Googlizable samples I find seem always to come with preinitialized hashes, arrays, etc. with sample calls to print them out. I just didn't find more practical examples this afternoon. Profuse thanks!

ddavison Over a year ago

and welcome to ruby! i myself came from Java and C++, and i am loving every minute that i play with ruby.. :)

Jörg W Mittag Over a year ago

This won't work, because you are always setting and getting the same key. Since you are both learning, I'll leave it to you to figure out why.

ddavison Over a year ago

yes @JörgWMittag, i'm aware of it :) i'm only duping what OP wanted.

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