Is there a CallByName equivalent for global functions?

Question

I want to do this: "If there's a module X containing a function Y then call it, otherwise don't."

I'm aware that I can use CallByName(Object, MethodName, ...) to call a method or property of an object instance.

Is it possible to call a global sub/function which is not bound to an object?

//Module1
Public Sub DoSomething
End Sub

//Module2
Public Sub TriggerDoSomething
  On Error Resume Next
  CallByName2 "Module1", "DoSomething", ...
End Sub

I know, it would be better to refactor my code to wrap DoSomething into a class, but currently this is not possible as it would break the code of my coworkers in a way that could not be fixed in a few hours.

Answer 1

Could conditionnal compilation be ok for your problem ?

//Module2
Public Sub TriggerDoSomething
    #If DoSomething_IsPresent Then
        DoSomething
    #End if
End Sub

Then in your project settings you would add the following conditionnal compilation arguments :

• If DoSomething is present : DoSomething_IsPresent = -1
• If DoSomething is not present : DoSomething_IsPresent = 0

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By the way, be careful with the "On Error Resume Next" in :

//Module2
Public Sub TriggerDoSomething
  On Error Resume Next
  CallByName2 "Module1", "DoSomething", ...
End Sub

If DoSomething is present in Module1 but has an unhandled error you won't notice it.

Answer 2

It really would be easier to CallByName a class - can't you just wrap the module(s) with a class that redirects the calls to the module?

It's possible to call routines in modules by name using a FunctionDelegator. This is explained in Matt Curland's excellent book Advanced Visual Basic 6.

Googling might find you some hacks using CallWindowProc, but Matt Curland says that's dangerous. Which is pretty much the final word on the matter :)

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EDIT: RS Conley's answer is don't use a module, use a class that has a instancing property of GlobalMultiUse and you will be able to use CallbyName. This will work if your code is in a DLL rather than an EXE. RS Conley suggests in any case it is more flexible to have a minimal EXE with nearly all functionality in a DLL: this may well be true.

Answer 3

Don't use a module, use a class that has a instancing property of GlobalMultiUse and you will be able to use CallbyName