Inheritence and overloading operators

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  • Noodle
    #1

    Inheritence and overloading operators

    Hi Guys, not sure if anyone can help me on this one but......

    I have a class that I overload the equality operator (=). I also have
    a class that inherits from this first class which has extra attributes
    that i need to check to see if they are equal for the previous
    overload to work correctly. No my question is how do I do this? The
    obvious answer is to overload the overloaded operator and then copy
    the comparison routine from the inherited object and copy it to the
    new routine in the derived class, then add any extra comparisons.

    although this will work for me, it adds the posibility that the base
    class will be updated and derived classes that inherit from it will
    not have a working comparison check as the new code added to the
    original class will need to be copied to the new one.

    Now I know that I can use mybase to access the base object of an
    inherited object but as the overloaded function takes in two arguments
    of type (derived class) how can I access the base class to do the
    comparison.

    Thanks in advance,

    Dean.

    Tags: None
    • Phill W.
      #2
      Re: Inheritence and overloading operators

      Noodle wrote:
      I have a class that I overload the equality operator (=). I also have
      a class that inherits from this first class which has extra attributes
      that i need to check to see if they are equal for the previous
      overload to work correctly. No my question is how do I do this? The
      obvious answer is to overload the overloaded operator and then copy
      the comparison routine from the inherited object and copy it to the
      new routine in the derived class, then add any extra comparisons.
      I think you mean /Overridden/, not Overloaded.
      You override methods in base classes where the arguments are the same,
      but you want them to do something different
      You Overload methods (in the same class or its Superclass) when you want
      to do the same /sort/ of thing, but supplying different arguments.
      although this will work for me, it adds the posibility that the base
      class will be updated and derived classes that inherit from it will
      not have a working comparison check as the new code added to the
      original class will need to be copied to the new one.
      So ask the base class if /it/ think things are the same, based on /its/
      view of the world and, if it says that every thing's OK, then "second
      guess" it, based on the subclasses view of things. (I haven't done
      overloaded operators yet, but here's the same idea with functions):

      Class Super
      Public Property X() as ...
      Public Property Y() as ...

      Public Overridable Function Equals( _
      other as Super _
      ) as Boolean
      If Me.X <other.X Then
      Return False
      End If
      If Me.Y <other.Y Then
      Return False
      End If
      Return True
      End Function
      End Class

      Class Subb
      Public Property Z() as ...

      Public Overrides Function Equals( _
      other as Subb _
      ) as Boolean
      If Not MyBase.Equals( other ) Then
      Return False
      End If

      If Me.Z <other.Z Then
      Return False
      End If

      Return True
      End Function
      End Class

      HTH,
      Phill W.

        Comment

        • Noodle
          #3
          Re: Inheritence and overloading operators

          On 15 Mar, 12:22, "Phill W." <p-.-a-.-w-a-r...@-o-p-e-n-.-a-c-.-u-k>
          wrote:
          Noodle wrote:
          I have a class that I overload the equality operator (=). I also have
          a class that inherits from this first class which has extra attributes
          that i need to check to see if they are equal for the previous
          overload to work correctly. No my question is how do I do this? The
          obvious answer is to overload the overloaded operator and then copy
          the comparison routine from the inherited object and copy it to the
          new routine in the derived class, then add any extra comparisons.
          >
          I think you mean /Overridden/, not Overloaded.
          You override methods in base classes where the arguments are the same,
          but you want them to do something different
          You Overload methods (in the same class or its Superclass) when you want
          to do the same /sort/ of thing, but supplying different arguments.
          >
          although this will work for me, it adds the posibility that the base
          class will be updated and derived classes that inherit from it will
          not have a working comparison check as the new code added to the
          original class will need to be copied to the new one.
          >
          So ask the base class if /it/ think things are the same, based on /its/
          view of the world and, if it says that every thing's OK, then "second
          guess" it, based on the subclasses view of things. (I haven't done
          overloaded operators yet, but here's the same idea with functions):
          >
          Class Super
          Public Property X() as ...
          Public Property Y() as ...
          >
          Public Overridable Function Equals( _
          other as Super _
          ) as Boolean
          If Me.X <other.X Then
          Return False
          End If
          If Me.Y <other.Y Then
          Return False
          End If
          Return True
          End Function
          End Class
          >
          Class Subb
          Public Property Z() as ...
          >
          Public Overrides Function Equals( _
          other as Subb _
          ) as Boolean
          If Not MyBase.Equals( other ) Then
          Return False
          End If
          >
          If Me.Z <other.Z Then
          Return False
          End If
          >
          Return True
          End Function
          End Class
          >
          HTH,
          Phill W.
          Hi Phill, yeah I meant overrides (doh). What you've suggested wont
          work as to overload an operator you have to have arguments for each
          class at the side of the operator in the expression.

          eg -

          Public Shared Operator =(ByVal olhs As CampaignDeal, ByVal orhs As
          CampaignDeal) As Boolean


          This means that I do not have access to the mybase functionality for
          the passed in arguments. I have figured it out now anyway, to compare
          the base class I do a directcast of the two arguments to the inherited
          class type and compare those, then if they equal start checking any
          attributes that the derived class has extra.

            Comment

            • Noodle
              #4
              Re: Inheritence and overloading operators

              On 15 Mar, 13:01, "Noodle" <d...@headnoodl e.comwrote:
              On 15 Mar, 12:22, "Phill W." <p-.-a-.-w-a-r...@-o-p-e-n-.-a-c-.-u-k>
              wrote:
              >
              >
              >
              >
              >
              Noodle wrote:
              I have a class that I overload the equality operator (=). I also have
              a class that inherits from this first class which has extra attributes
              that i need to check to see if they are equal for the previous
              overload to work correctly. No my question is how do I do this? The
              obvious answer is to overload the overloaded operator and then copy
              the comparison routine from the inherited object and copy it to the
              new routine in the derived class, then add any extra comparisons.
              >
              I think you mean /Overridden/, not Overloaded.
              You override methods in base classes where the arguments are the same,
              but you want them to do something different
              You Overload methods (in the same class or its Superclass) when you want
              to do the same /sort/ of thing, but supplying different arguments.
              >
              although this will work for me, it adds the posibility that the base
              class will be updated and derived classes that inherit from it will
              not have a working comparison check as the new code added to the
              original class will need to be copied to the new one.
              >
              So ask the base class if /it/ think things are the same, based on /its/
              view of the world and, if it says that every thing's OK, then "second
              guess" it, based on the subclasses view of things. (I haven't done
              overloaded operators yet, but here's the same idea with functions):
              >
              Class Super
              Public Property X() as ...
              Public Property Y() as ...
              >
              Public Overridable Function Equals( _
              other as Super _
              ) as Boolean
              If Me.X <other.X Then
              Return False
              End If
              If Me.Y <other.Y Then
              Return False
              End If
              Return True
              End Function
              End Class
              >
              Class Subb
              Public Property Z() as ...
              >
              Public Overrides Function Equals( _
              other as Subb _
              ) as Boolean
              If Not MyBase.Equals( other ) Then
              Return False
              End If
              >
              If Me.Z <other.Z Then
              Return False
              End If
              >
              Return True
              End Function
              End Class
              >
              HTH,
              Phill W.
              >
              Hi Phill, yeah I meant overrides (doh). What you've suggested wont
              work as to overload an operator you have to have arguments for each
              class at the side of the operator in the expression.
              >
              eg -
              >
              Public Shared Operator =(ByVal olhs As CampaignDeal, ByVal orhs As
              CampaignDeal) As Boolean
              >
              This means that I do not have access to the mybase functionality for
              the passed in arguments. I have figured it out now anyway, to compare
              the base class I do a directcast of the two arguments to the inherited
              class type and compare those, then if they equal start checking any
              attributes that the derived class has extra.- Hide quoted text -
              >
              - Show quoted text -
              damn done it again, i mean override :(

                Comment

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