Multiple Inheritance

• What if I want to build a tree-farm
  • This is a farm with a sawmill.
  • It should inherit CanProduce and Produce from the sawmill.
  • It should inherit FoodBonus from the farm.
• The syntax is simple
  • class TreeFarmT: public Farm, public Sawmill
• There is a problem however
  • Which version of Type and which warehouse will be referenced?
  • This is called the Diamond Problem
  • Because of this, some langaguaged do not allow multiple inheritance.
• Unfortunately the syntax from above will not compile.
• So the keyword virtual can be added to the inheritance chain.
  • class FarmT: virtual public BonusBuildingT
  • class SawmillT: public virtual ProductionBuildingT
  • class TreeFarmT: public Farm, public Sawmill
• Meyers says for correct behavior that every public inheritance should be virtual.
  • But this adds time complexity.
  • And space complexity.
• Names are more complex too.
  • Sometimes you need base.childa.chldb.FunctionName()
• He says to avoid this type of multiple inheritance whenever possible.
  • But use it if you need it.
  • But if you use virtual base classes, avoid placing data in the base class.