AndAlso/OrElse in VBA

Question

I'm trying to get a lazy evaluation with 'And' in my Excel macro by doing the following:

If Not myObject Is Nothing *And* myObject.test() Then
    'do something'
Else
    'do something else'
End If

I know lazy evaluation exists in VB.NET as AndAlso and OrElse but cannot find anything similar in VBA. If lazy evaluation does not exist in VBA, what's the best way to structure the code so that it will evaluate the way I expect?

Answer 1

The only short circuiting (of a sort) is within Case expression evaluation, so the following ungainly statement does what I think you're asking;

Select Case True
    Case (myObject Is Nothing), Not myObject.test()
        MsgBox "no instance or test == false"
    Case Else
        MsgBox "got instance & test == true"
    End Select
End Sub

Answer 2

This is an old question, but this issue is still alive and well. One workaround I've used:

Dim success As Boolean       ' False by default.

If myObj Is Nothing Then     ' Object is nothing, success = False already, do nothing.
ElseIf Not myObj.test() Then ' Test failed, success = False already, do nothing.
Else: success = True         ' Object is not nothing and test passed.
End If

If success Then
    ' Do stuff...
Else
    ' Do other stuff...
End If

This basically inverts the logic in the original question, but you get the same result. I think it's a cleaner solution than the others here that only use If statements. The solution using a Select statement is clever, but if you want an alternative using only If statements, I think this is the one to use.

Answer 3

Or you could create a function that takes your object as a parameter and returns boolean for either case. That's what I usually to.

i.e.

if Proceed(objMyAwesomeObject) then
       'do some really neat stuff here
else
       'do something else, eh
end if
...
end sub

private function Proceed(objMyAwesomeObject as Object)
     if not objMyAweseomeObject is nothing then
            Proceed = true
     elseif objMyAwesomeObject.SomeProperty = SomeValue then
            Proceed = true
     else
            Proceed = false
     endif
end function