How to call a method to load class variable in Ruby?

Question

The data is loaded once because it takes a while to load, doesn't change, and is shared. This is a static class: I am not using any instances.

class Foo
  @@ data = self.load_data

  def self.load_data
    .
    . 
    .
  end

  def self.calculate
    .
    .
  end
end

This throws an error NoMethodError: undefined method 'load_data' for Foo:Class because load_data appears after the assignment.

I don't think initialize will work because I am not using f = Foo.new. I am using it as Foo.calculate.

Is it necessary to declare load_data before calling it? Or is there a better approach?

dbenhur · Accepted Answer · 2012-04-03 15:20:00Z

2

Yes Foo.load_data doesn't exist yet at the point you call it.

A better pattern might be to have an accessor for @@data which auto-memoizes.

class Foo
  def self.data
    @@data ||= load_data
  end
  def data; self.class.data; end # if you need it in instances too

  def self.load_data
    ...
  end

  def self.calculate
    data.each {} # or whatever would have used @@data
  end
end

edited Apr 3, 2012 at 15:20

answered Apr 3, 2012 at 5:19

dbenhur

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Comments

Soundar Rathinasamy · Accepted Answer · 2012-04-03 05:12:29Z

0

Load data by class level function call.

class Foo
  def self.load_data
    .
    . 
    .
    @data = value
  end

  def self.calculate
   #use @data in this function.
   .
   .
  end
end

#first load data
Foo.load_data

#then process data
Foo.calculate

answered Apr 3, 2012 at 5:12

Soundar Rathinasamy

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2 Comments

B Seven Over a year ago

Foo.calculate is run through a cron job, so there is no good time to call load_data. In this case it's better to auto-load somehow...

Soundar Rathinasamy Over a year ago

then call load_data from calculate method.

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