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vbaparamarray

Validate that ParamArray contains the right types of parameters

I'm trying to use ParamArray to pass different kinds of parameters to the same function to mimic Function Overloading.

  • One single String
  • One Workbook object, one String as well as an Integer

So user may pass different arguments to the same function:

Function func(ParamArray params() As Variant)

blah = func("This is a string")

blah = func(wbSource, "SheetName", iRow)

Is there a way to validate the types of arguments? I need to make sure that params() contains the right types of arguments (one workbook, one string and one integer).

For sure I can hard code with a bunch of If-Else, but what if in the future there are more arguments? I'm thinking about using TypeName() to dump the types to a String array and then do the comparison. But this still seems to be cumbersome. Is there a better way to achieve this?

BTW I don't think Optional is a good idea because who knows how many arguments there will be?

Solution

  • I'm trying to use ParamArray to pass different kinds of parameters to the same function to mimic Function Overloading.

    IMO that's a terrible idea: you lose the compile-time check on argument counts, lose intellisense at call sites telling you what the expected parameters & types are.

    C# started off with method overloading, and evolved to support optional parameters. Now that optional parameters are supported, method overloading is, in C#, simply an alternative to optional parameters, and vice-versa.

    VBA supports optional parameters, but not method overloading. Big deal: you can use optional parameters and achieve the exact same as C#'s alternative to method overloading.

    ParamArray isn't an option.

    The answer to "is there a way to validate the types of the arguments" is - YES! Let the compiler do its job!

    I don't think Optional is a good idea because who knows how many arguments there will be?

    If you don't, nobody knows! A method with too many arguments is often a code smell: is the method responsible for too many things? Does the name accurately convey everything it does? Hard to tell with what you've supplied, but I'd argue that if you're writing a method and you don't know how many arguments it is going to need, how do you know what that method needs to do?