Using Optional Parameters in VBScript

One method for simulating optional arguments in VBScript that has not been discussed in any 4Guys article, though, is the use of the class-as-function-call method. This method is very popular with component developers. You could say that SoftArtisan's entire FileUp component is one class-as-function call. What I mean by this is instead of saying something like this (which VBScript won't even allow but VB and C++ do):

To use a class-as-function call, we first need to create a class. This is a feature that VBScript started supporting back in version 5.0. To learn what version of VBScript you are running, check out: Determining the Server-Side Scripting Language and Version.

To utilize the class-as-function method, our class should contain a member variable for each parameter. Each function and subroutine that supports optional parameters should accept zero parameters. While this may seem a tad confusing, check out the code below, which will (hopefully) clear everything up!

class NodePathHtmlGenerator
	Dim theNode
	Dim showImage
	Dim showLinks
	Dim forceVerdana

	function RenderHtml
		if IsEmpty(showImage) then showImage = true
		if IsEmpty(showLinks) then showLinks = true
		if IsEmpty(forceVerdana) then forceVerdana = true
		...
	end function
end class

To call this function simply create an instance of the class, set whatever properties you care to, and then call the main method:

Of course the above approach is three lines longer than it could be, but once you're commonly using more than a couple parameters (and not often using more than a few other parameters), the clarity of named parameters outweighs the extra typing.

To ensure that the properties were of the correct data type and format, you'd likely want to create the class's properties as Private and then use Property Let and Property Get statements to read and write the values, respectively. Also note that you can have more than one function or subroutine in the class. Just be sure to create class properties for each of the optional parameters that each function or subroutine may need.

Happy Programming!