CODEWITHSUNDEEP
rubyarraysclasstypesmethods
Jon J
Jon J

Reputation: 491

Ruby object returned from method loses class type (reverts to base class array)

In the following code, the issue is that after calling method .find_name on an object type of LogsCollection, the returned object becomes a native array and does not remain type LogsCollection. I believe the correct approach might be to create a constructor/initializer that accepts an array and return a brand new object of the correct type. But I am not sure there is not a better way to accomplish this?

Can a Ruby-pro eyeball this code and suggest (at the code level) the best way to make the returned object from .find_name remain type LogsCollection (not array)?

class Log
    attr_accessor :name, :expense_id, :is_excluded, :amount, :paid_to
    def initialize(name, expense_id, is_excluded, amount, paid_to)
        @name = name
        @expense_id = expense_id
        @is_excluded = is_excluded
        @amount = amount
        @paid_to = paid_to
    end
end

class LogsCollection < Array
    def names
        collect do |i|
            i.name
        end
    end

    def find_name(name)
        @name = name
        self.select { |l| l.name == @name }
    end
end

logs = LogsCollection.new
logs.push(Log.new('Smith', 1, false, 323.95, nil))
logs.push(Log.new('Jones', 1, false, 1000, nil))

logs = logs.find_name('Smith')
puts logs.count
unless logs.empty?
    puts logs.first.name # works since this is a standard function in native array
    puts logs.names # TODO: figure out why this fails (we lost custom class methods--LogsCollection def find_name returns _native_ array, not type LogsCollection)
end

Final code post-answer for anyone searching (note the removal of base class < array):

class Log
    attr_accessor :name, :expense_id, :is_excluded, :amount, :paid_to
    def initialize(name, expense_id, is_excluded, amount, paid_to)
        @name = name
        @expense_id = expense_id
        @is_excluded = is_excluded
        @amount = amount
        @paid_to = paid_to
    end
end

class LogsCollection
    attr_reader :logs

    def initialize(logs)
        @logs = logs
    end

    def add(log)
        @logs.push(log)
    end

    def names
        @logs.collect { |l| l.name }
    end

    def find_name(name)     
        LogsCollection.new(@logs.select { |l| l.name == name })
    end
end

logs = LogsCollection.new([])

logs.add(Log.new('Smith', 1, false, 323.95, nil))
logs.add(Log.new('Jones', 1, false, 1000, nil))
puts logs.names

puts '--- post .find_name ---'

puts logs.find_name('Smith').names

Upvotes: 0

Views: 689

Answers (1)

Michael Kohl
Michael Kohl

Reputation: 66837

As you can see in the docs Enumerable#select with a block always returns an array. E.g.

{:a => 1, :b => 2, :c => 3}.select { |k,v | v > 1 }
=> [[:b, 2], [:c, 3]]

What you could do is have some sort of constructor for LogsCollection that wraps up a normal array as a LogsCollection object and call that in find_name.

As requested here's an example class (I'm at work and writing this while waiting for something to finish, it's completely untested):

class LogsCollection
  attr_reader :logs

  def initialize(logs)
    @logs = logs
  end

  def names
    @logs.collect { |i| i.name }
  end

  def find_name(n)
    name = n
    LogsCollection.new(@logs.select { |l| l.name == n })
  end

  # if we don't know a method, forward it to the @logs array
  def method_missing(m, *args, &block)
    @logs.send(m, args, block)
  end
end

Use like

lc = LogsCollection.new
logs = lc.logs.find_name('Smith')

Upvotes: 2

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