Help refactor function that takes lots of arguments.

Question

Hi all,

I was wondering if anyone would be able to help me refactor some code that I wrote a while ago. I wrote a wrapper for a COM object that only excepted strings as input, so in good OOP practice I wrapped the string up in a function so that it was easier to build and call.

I was just wondering if anyone could think of a better way to do the following code.

   Public Function OpenTable(ByVal TablePath As String, Optional ByVal OpenAs As String = Nothing, _
            Optional ByVal Hide As Boolean = False, Optional ByVal AsReadOnly As Boolean = False, _
            Optional ByVal Interactive As Boolean = True, Optional ByVal Password As String = Nothing, _
            Optional ByVal NoIndex As Boolean = False, Optional ByVal ViewAutomatic As Boolean = True) As TableInfo

            If String.IsNullOrEmpty(TablePath) Then
                Throw New ArgumentNullException("TablePath", "TablePath cannot be null or empty")
            End If

            Dim Builder = New StringBuilder("Open Table ")
            Builder.AppendFormat("{0}{1}{2}", ControlChars.Quote, TablePath, ControlChars.Quote)

            If (Not String.IsNullOrEmpty(OpenAs)) Then Builder.AppendFormat(" as {0} ", OpenAs)
            If (Hide) Then Builder.Append(" Hide ")
            If (AsReadOnly) Then Builder.Append(" ReadOnly ")
            If (Interactive) Then Builder.Append(" Interactive ")
            If (Not String.IsNullOrEmpty(Password)) Then Builder.AppendFormat(" Password {0} ", Password)
            If (NoIndex) Then Builder.Append(" NoIndex ")
            If (ViewAutomatic) Then Builder.Append(" View Automatic ")

            MyComApp.Do(Builder.ToString)

            Dim FileInfo = New IO.FileInfo(TablePath)
            Return New TableInfo(FileInfo.Name.Substring(0, InStrRev(FileInfo.Name, ".") - 1))
        End Function

The amount of arguments that the function has to take is my biggest worry. This one is not too bad but there are some other functions that I may have to make in the future that will take a lot more arguments, so I'm mainly looking for better ways to build large argument functions.

Thanks.

Answer 1

Since i dont know your programming language, im gonna keep this to pseudo code, but my general answer is to use ann array as single parameter:

function OpenTable( options As array) {
    if (options is not array or options is empty) {
        Throw exception
    }
    return_string = "";
    if ( key is set ('readOnly', options) and is not empty) {
        return_string = return_string + ' readonly';
    }
    // repeat last 3 lines for all your params
}

Ok the last part of your function doesnt make sense to me, but the idea of array of params should come across i think. Good luck.

Answer 2

One way to handle functions that can take lots of arguments is to create a new object type whose sole purpose is to hold arguments for that function. Then you create a new object of that type, set the properties as needed, then pass that one object reference to your OpenTable function.

Answer 3

In this case it seems many of the parameters are just 'configuration values' (which end up being strings), you could modify it to accept a single class for all the configuration that you prepare before the call and that will return you the string accordingly.

Something like

class COMConfiguration {
    private bool Hide = false;
    private bool AsReadOnly = false;
    //and so on...

    public void setHide(bool v) { Hide = v; }

    //only setters

    public string getConfigString() {
        StringBuilder sb = new StringBuilder();
        if (Hide) { sb.Append(" Hide "); }
        if (AsReadOnly) { sb.Append(" ReadOnly "); }
        //and so on
        return sb.ToString()
    }
}

Answer 4

You can switch all your boolean parameters to a single parameter of an enum type, marked as Flags. Here's an example declaration:

' Define an Enum with FlagsAttribute.
<FlagsAttribute( )> _
Enum TableOptions as Short
    Hide = 1
    AsReadOnly = 2
    Interactive = 4
    NoIndex = 8
    ViewAutomatic = 16
End Enum