add abstract base class for set_byte and set_slot called setter

lib/register/instructions/setter.rb

@@ -0,0 +1,29 @@
+module Register
+  # Setter is a base class for set instructions (SetSlot and SetByte , possibly more coming)
+  #
+  # The instruction that is modelled is loading data from an array into a register
+  #
+  # Setter has a
+  # - Register that the data is moved to
+  # - an array where the data comes from
+  # - and (array) index
+  class Setter < Instruction
+
+    # If you had a c array and index offset
+    # the instruction would do array[index] = register
+    # So Setter means the register (first argument) moves to the slot (array and index)
+    def initialize source , register , array , index
+      super(source)
+      @register = register
+      @array = array
+      @index = index
+      raise "index 0 " if index == 0
+      raise "Not integer or reg #{index}" unless index.is_a?(Numeric) or RegisterValue.look_like_reg(index)
+      raise "Not register #{register}" unless RegisterValue.look_like_reg(register)
+      raise "Not register #{array}" unless RegisterValue.look_like_reg(array)
+    end
+    attr_accessor :register , :array , :index
+
+  end
+
+end