Start work on Port class

port.rb

@@ -0,0 +1,83 @@
+## Represents an IO port of a device
+
+class Port
+  include Comparable
+
+  # @!attribute [r] val
+    # @return [Integer] the current value of the port
+  attr_reader :val
+
+  # Returns a new instance of Port
+  # @param name [String] The string name of the port
+  def initialize(name="")
+    @connected=[]
+    @propagating=false
+    @val=0
+    @strname=name
+  end
+
+  # Sets the port's value
+  # @param val [Integer] The new value for the port
+  # @return [void]
+  def setval(val)
+    # Prevent infinite loops when the connected port calls back when propagating.
+    if !@propagating
+      @val=val
+      @propagating=true
+      propagate()
+      @propagating=false
+    end
+  end
+
+  # Connects this port to another port
+  # @param port [Port] The port to connect to
+  # @return [void]
+  def connect(port)
+    @connected.push port
+    port.connect_back(self)
+  end
+
+  # Returns a string representation for debugging
+  # @return [String] String name of the port, or super if none
+  def to_s()
+    return super if @strname==""
+    return @strname
+  end
+
+  # Method for Comparable module to use for comparasions.
+  # @param obj [Object] Object to compare to
+  # @return [void]
+  def <=>(obj)
+    if obj.class==Port
+      return @val<=>obj.val
+    elsif obj.is_a? Integer
+      return @val<=>obj
+    end
+  end
+
+  # Used by connect when setting up bidirectional connection.
+  # @api private
+  # @param (see #connect)
+  # @return [void]
+  def connect_back(port)
+    @connected.push port
+  end
+
+  private
+
+  # Propagates the value to all connected ports
+  # @return [void]
+  def propagate()
+    @connected.each do |port|
+      port.setval(@val)
+    end
+  end
+
+end
+
+a=Port.new("a")
+b=Port.new("b")
+c=Port.new("c")
+a.connect(b)
+b.connect(c)
+a.setval(10)

spec/port_spec.rb

@@ -0,0 +1,39 @@
+require_relative "../port.rb"
+
+describe Port do
+  it "should set the port's value when we call setval" do
+    a=Port.new
+    a.setval(1)
+    expect(a).to eq 1
+  end
+  it "should propagate values when we call setval" do
+    a=Port.new
+    b=Port.new
+    c=Port.new
+    d=Port.new
+
+    #connect A-B and C-D
+    a.connect(b)
+    c.connect(d)
+
+    a.setval(1)
+    c.setval(2)
+    expect(a).to eq 1
+    expect(b).to eq 1
+    expect(c).to eq 2
+    expect(d).to eq 2
+
+    #connect them all together
+    b.connect(c)
+    a.setval(3)
+    expect(a).to eq 3
+    expect(b).to eq 3
+    expect(c).to eq 3
+    expect(d).to eq 3
+    d.setval(4)
+    expect(a).to eq 4
+    expect(b).to eq 4
+    expect(c).to eq 4
+    expect(d).to eq 4
+  end
+end