Question New to operator overloading. Am I doing it right?

[munkyeetr]

I am creating a RomanNumeral class (which I will post soon for people to look at), and I currently implementing Operator Overloading so math operations can be perform using the objects. I have never done this before and would like some feedback whether I am doing or correctly or not.

Each object has the following properties (among others) that return a value:

Object.Number as Integer
Object.Numeral as String    ' Roman numeral representation of .Number

And the class has 3 constructors:

New()                      ' Values are set to 0
New(number as Integer)     ' Values are set to number
New(numeral as String)     ' Values are set to numeral

So far I have only overloaded the + (addition) operator. and I have tried to make it so operations can be performed between multiple RN's, Integers and RN's, Strings and RN's. They work as I expect in testing so far, but I just want to see if I am making any glaring faux pas in their implementation.

Here are my current overloads:

   Public Shared Operator +(ByVal rn1 As RomanNumeral, ByVal rn2 As RomanNumeral) As RomanNumeral
        Try
            Return New RomanNumeral(rn1.Number + rn2.Number)
        Catch ex As System.OverflowException
            Dim rv As RomanNumeral = New RomanNumeral
            rv.m_Malformation = MalformationError.ValueOverflow
            Return rv
        End Try
    End Operator

    Public Shared Operator +(ByVal rn As RomanNumeral, ByVal number As Integer) As RomanNumeral
        Try
            Return New RomanNumeral(rn.Number + number)
        Catch ex As System.OverflowException
            Dim rv As RomanNumeral = New RomanNumeral
            rv.m_Malformation = MalformationError.ValueOverflow
            Return rv
        End Try
    End Operator

    Public Shared Operator +(ByVal number As Integer, ByVal rn As RomanNumeral) As RomanNumeral
        Try
            Return New RomanNumeral(rn.Number + number)
        Catch ex As System.OverflowException
            Dim rv As RomanNumeral = New RomanNumeral
            rv.m_Malformation = MalformationError.ValueOverflow
            Return rv
        End Try
    End Operator

    Public Shared Operator +(ByVal rn As RomanNumeral, ByVal numeral As String) As RomanNumeral
        Dim rv As RomanNumeral = New RomanNumeral(numeral)
        Try
            Return New RomanNumeral(rn.Number + rv.Number)
        Catch ex As System.OverflowException
            rv.Number = 0
            rv.m_Malformation = MalformationError.ValueOverflow
            Return rv
        End Try
    End Operator

    Public Shared Operator +(ByVal numeral As String, ByVal rn As RomanNumeral) As RomanNumeral
        Dim rv As RomanNumeral = New RomanNumeral(numeral)
        Try
            Return New RomanNumeral(rn.Number + rv.Number)
        Catch ex As System.OverflowException
            rv.Number = 0
            rv.m_Malformation = MalformationError.ValueOverflow
            Return rv
        End Try
    End Operator

Thanks, any input is appreciated.

 

[JohnH]

I would

• define it as a Structure, not a Class,
• implement Parse/TryParse methods for String conversions, and remove String constructor, but also add CType operator for String,
• override ToString method, and remove Numeral property.
• avoid math operators between String operands.

 

[jmcilhinney]

Your operators seem OK at a glance. I'd suggest having Parse and TryParse methods for converting Strings though, rather than a constructor.

 

[munkyeetr]

Thanks for the input.

Here's a Pastebin of my class file RomanNumeral.vb
The strings are parsed and evaluated by an internal function [ ps_MalformedNumeral ] that is called by the constructor and Property Set. Correct me if I am wrong, but construction and assignments like the following wouldn't be applicable to TryParse because it tries to create an Integer out of a string of numeric digits, no?:

Dim rn as RomanNumeral = New RomanNumeral("XXII")  ' Create a RN with a value of 22
rn.Numeral = "CCCLV"                               ' Reassign to 355

After I get the operator overloads finished I would like to post the class in a separate thread to get feedback and suggestions.
Thanks for looking and please correct me if i am wrong in my assumptions.

Munky

 

[jmcilhinney]

Consider the BigInteger structure. It has Parse and TryParse methods for conversion of Strings but no constructor that accepts a String argument. I would also agree that a structure is more appropriate than a class. In that case, setting the Numeral property wouldn't make sense because creating a new value would have the same effect. Notice that all numeric types in the Framework are structures, as are various other small types that represent values, e.g. DateTime and Boolean.

 

[munkyeetr]

Consider the BigInteger structure. It has Parse and TryParse methods for conversion of Strings but no constructor that accepts a String argument. I would also agree that a structure is more appropriate than a class. In that case, setting the Numeral property wouldn't make sense because creating a new value would have the same effect. Notice that all numeric types in the Framework are structures, as are various other small types that represent values, e.g. DateTime and Boolean.

I will take a look at that. Thanks.