playing-with-structs

playing-with-structs.rb

# POODR page 28
Wheel = Struct.new(:rim, :tire)
def wheelify(data)
  data.collect {|cell| Wheel.new(cell[0], cell[1])}
end

# POODR Page 32
class Gear
  attr_reader :chainring, :cog, :wheel
  def initialize(chainring, cog, rim, tire)
    @chainring = chainring
    @cog = cog
    @wheel = Wheel.new(rim, tire)
  end
...
  Wheel = Struct.new(:rim, :tire) do
    def diameter
      rim + (tire * 2
    end
  end
end

# Me playing around
> Agent  = Struct.new(:listing_id, :selling_id)
=> Agent
> t1 = Agent.new(1, 2)
=> #<struct Agent listing_id=1, selling_id=2>
> t1.listing_id
=> 1
> t2 = Agent.new(1, 3)
=> #<struct Agent listing_id=1, selling_id=3>
> t3 = Agent.new(2, 4)
=> #<struct Agent listing_id=2, selling_id=4>
> t4 = Agent.new(2, 5)
=> #<struct Agent listing_id=2, selling_id=5>
> ts = [t1, t2, t3, t4]
=> [#<struct Agent listing_id=1, selling_id=2>, #<struct Agent listing_id=1, selling_id=3>, #<struct Agent listing_id=2, selling_id=4>, #<struct Agent listing_id=2, selling_id=5>]
> selling_ids = ts.select { |t| t.listing_id == 1 }.map &:selling_id
=> [2, 3]
> ts.select { |t| selling_ids.include? t.listing_id }.map(&:selling_id)
=> [4, 5]
> ts.select { |t| selling_ids.include? t.listing_id }.map(&:selling_id).count
=> 2