Ruby – undefined method … for class (NoMethodError)


I'm just startin to learn ruby and I'm writing a simple program, but I've got an error undefined method 'send_for_beer' for Person:Class (NoMethodError)
Here is a code:

class Person
    @iq = 0
    @speed = 0
    @power = 0
    @beauty = 0
    def initialize (iq, speed, power, beauty)
        @iq = iq
        @speed = speed
        @power = power

    def send_for_beer
        result @iq * 2 + @speed * 10 + @power * 5 + @beauty
        return result

number_of_people = 3
person_array =, Person)
n = 0
beer_person = 0
beer_cof = 0
number_of_people.times do 

    person_array.push(, speed, power, beauty))

    if person_array[n].send_for_beer > beer_cof     <-----here is an error
        beer_cof = person_array[n].send_for_beer
        beer_person = n
    n = n+1

Best Solution

Here's your problem:

person_array =, Person)

In short, don't make array like this. Use the [] literal syntax. What this returns is:

[Person, Person, Person]

That is 3 references to the Person class, not instances. Then later you do:

person_array.push(, speed, power, beauty))

And you end up with:

[Person, Person, Person, person_instance]

So when you iterate through and call send_for_beer on that first item, it does have that method because send_for_beer is an instance method that you are calling erroneously on a class object.

The fix here is to simply assign person_array to an empty array literal, and then push things to it.

person_array = []

And a minor style note: << is usually preferred to Array#push, making the filling of the array look more like this.

person_array <<, speed, power, beauty)

Ruby also support implicit return of the last expression in a method. So you do not need to return result. Instead, simply calulate the return value as the only line in the method.

def send_for_beer
  @iq * 2 + @speed * 10 + @power * 5 + @beauty

Instance variables don't quite work like that either. When you have @name in the class body directly, you are not initializing instance variables for each instance. You are actually setting instance variable on the class object (which is weird, I know). What you actually need to do is set them from any instance method, typically initialize, which you are doing here. So you can totally remove the instance variable setting at the class level here.

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