How to call instance variables in ruby

Question

I have recently learned how to create classes, although I am not ENTIRELY sure where and why I should use them. I'd use them to create objects, which have similar methods/properties.

I tried making a gag code, but I stumbled upon a question I can't find an answer to.

class Person
  def initialize(name,health)
    @name = name
    @hp = health
  end

  def kick
    @hp -= 1
    if (@hp <= 0)
      puts "#{@name} got REKT!"
    end
  end

end

#Friends
michael = Person.new("Michael", 10)

10.times { michael.kick }

Even though this code works, I'm wondering if it is possible to use/call mihchael's hp outside the class? Perhaps sort of like a hash? michael[@hp]? But this doesn't work, even if i set hp to be a global variable. Should all if/else statements who check object's properties be inside the class?

Thank you very much

i guess you are looking for attr_accessor. attr_accessor :hp — amalrik maia
– amalrik maia, Commented May 6, 2016 at 18:29
I would recommend reading about attr_accessor over at this SO question: stackoverflow.com/questions/4370960/… — Charles Caldwell
– Charles Caldwell, Commented May 6, 2016 at 18:31
Please paste your code as text, not a picture, to make it easier to modify. — nwk
– nwk, Commented May 6, 2016 at 18:35
Do you really expect readers who wish to modify your code to copy it manually, line-by-line? — Cary Swoveland
– Cary Swoveland, Commented May 6, 2016 at 18:50
What is "gag code"? Is it related to shutting someone up, pranks or choking? — Cary Swoveland
– Cary Swoveland, Commented May 6, 2016 at 18:57

tadman · Accepted Answer · 2016-05-06 18:38:32Z

5

The standard way to do this in Ruby is to create an accessor:

class Person
  attr_reader :name
  attr_reader :hp
end

Then outside the class you can call things like:

puts "#{michael.name} has only #{michael.hp} HP left"

The reason you create objects is to organize your code and data into logical contexts and containers.

answered May 6, 2016 at 18:38

tadman

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13 Comments

Cary Swoveland Over a year ago

...but if there are no accessors, all is not lost:

puts "#{michael.instance_variable_get(:@name)} has only #{michael.instance_variable_get(:@hp)} HP left" #=> "Michael has only 10 HP left"

. See Object#instance_variable_get.

tadman Over a year ago

@CarySwoveland True, but that's the equivalent of reaching into someone's pants to grab their keys. It's not very polite. An accessor is the best way to ask for permission, plus it means the class is free to change how those values are stored.

ruby_object Over a year ago

@tadman if attr_reader :keys is used then we do not hold the \@keys attribute in the pants pocket, but advertise it as 'the \@keys are on the hook next to the door'. You do not understand how attr_reader :keys works. Basically it tells interpreter do define def keys; \@keys ;end . So when you remove attr_reader and define method keys with you can easily have your changes done.

tadman Over a year ago

@ruby_object Now I'm even more confused what your objection here is. Yes, it's a class method and that's why I'm using it in the class context. This is textbook how it's done. If there was a mistake in a book I don't see how that's relevant.

tadman Over a year ago

@ruby_object If there's any misunderstanding here I think it's your understanding of the question. The question was "how do I access instance variables" and the most idiomatic answer is "use attr_reader". Yes, attr_reader is a class method, and obviously so since it's used to alter the properties of the class and introduce these new instance methods dynamically.

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