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It is generally accepted that it is a good programming practice to not use monolithic code, but to break functional units of code into separate subs or functions and call these from a control procedure. Functions are very useful for passing values back to the calling procedure, but functions return a single value so what if you want to get more than one value returned to you calling procedure?
I have often seen this topic raised in the Excel forums, a statement that a function cannot return multiple values, or a question on how to return multiple values. There are a number of ways to return multiple values, here I will show 3 such ways, with 2 variations on the last one.
The ways that I will cover are:
- Classes
- ByRefArguments
- UDTs
- Returning a UDT
- UDT as an Argument
Some of the codeI includes basic error handling to illustrate the point made earlier.
Classes
The first example here is using classes. Classes have properties that can be read, write, or read-write, they can have as many as you need, and they have methods which are essentially functions within the class. So it should be clear that by using a class, our control procedure can call a procedure that returns multiple values; any of the properties or functions could set any number of other properties; a call to a class can then read those properties to get multiple return values. An example class and calling procedure is shown in Figure 1.
Public Sub MultiplesClass()
Dim cls As clsPerson
On Error GoTo errhnd
Set cls = New clsPerson
cls.Name = "Jack"
cls.DoB = DateSerial(1976, 12, 3)
MsgBox cls.Name & " aged " & cls.Age & " years"
teardown:
Set cls = Nothing
Exit Sub
errhnd:
MsgBox Err.Number & "," & Err.Description
Resume teardown
End Sub
Private mAge As Long
Private mDoB As Date
Public Name As String
Public Property Let DoB(Value As Date)
mDoB = Value
mAge = Year(Date) - Year(mDoB)
If DateSerial(Year(Date), Month(mDoB), Day(mDoB)) >= Date Then
mAge = mAge - 1
End If
End Property
Public Property Get Age() As Long
Age = mAge
End Property
Figure 1 – Using a Class to Return Multiple Values
Byref Arguments
Perhaps the easiest way to return multiple values is to use arguments of the function to return amended or changed values. This method can use the return value to pass the function success status with the arguments returning the business variables. The one thing to note is that arguments that will be used to return values must be passed ByRef.
Figure 2 shows an example of returning multiple values using function arguments, also demonstrating the error handling.
Public Function MultiplesArgsCaller()
Dim myName As String
Dim myAge As Long
Dim isBlokeWoman As String
On Error GoTo errhandler:
myName = "John"
If Not MultiplesArgsCalled(myName, isBlokeWoman, myAge) Then
Err.Raise 19999
End If
MsgBox myName & " is a " & " is a " & myAge & " year old " & isBlokeWoman
myName = "Jane"
If Not MultiplesArgsCalled(myName, isBlokeWoman, myAge) Then
Err.Raise 19999
End If
MsgBox myName & " is a " & " is a " & myAge & " year old " & isBlokeWoman
myName = "Damien"
If Not MultiplesArgsCalled(myName, isBlokeWoman, myAge) Then
Err.Raise 19999
End If
MsgBox myName & " is a " & " is a " & myAge & " year old " & isBlokeWoman
teardown:
Exit Function
errhandler:
If Err.Number = 19999 Then Err.Description = myName & "is an unknown name"
MsgBox Err.Number & ", " & Err.Description
Resume teardown
End Function
Private Function MultiplesArgsCalled( _
ByVal Name As String, _
ByRef GenderType As String, _
ByRef Age As Long) As Boolean
MultiplesArgsCalled = True
Select Case Name
Case "John"
GenderType = "bloke"
Age = 45
Case "Jane"
GenderType = "woman"
Age = 36
Case Else
MultiplesArgsCalled = False
End Select
End Function
Figure 2 – Using a Function Arguments to Return Multiple Values
Returning a UDT
The third and fourth methods use user defined types (UDTs).
UDTs can be seen as mini, very basic, classes. They are a set of data elements within an encompassing object, any instance of a UDT will inherit all of those data elements. The elements within a type can be strongly type with the uual data types, or default to Variant. Interestingly, an elament within a UDT can be defined as a previously defined UDT, types within types, but that is another topic.
As with function arguments, the elements within a UDT can be used as read, write or read-write data elements, the values that are passed to the function can be separated from the values returned, or a value could be passed to the function, amended ther, and the changed value returned in the same UDT element.
The first of these two methods uses a UDT for the function type. Figure 3 shows an example of returning multiple values using a UDT as a function type.
Public Type Person
Gender As String
Age As Long
Success As Boolean
End Type
Public Function MultiplesUDTCaller()
Dim myName As String
Dim thisPerson As Person
Dim isBlokeWoman As String
On Error GoTo errhandler:
myName = "John"
thisPerson = MultiplesUDTCalled(myName)
If Not thisPerson.Success Then
Err.Raise 19999
End If
MsgBox myName & " is a " & " is a " & thisPerson.Age & " year old " & thisPerson.Gender
myName = "Jane"
thisPerson = MultiplesUDTCalled(myName)
If Not thisPerson.Success Then
Err.Raise 19999
End If
MsgBox myName & " is a " & " is a " & thisPerson.Age & " year old " & thisPerson.Gender
myName = "Damien"
thisPerson = MultiplesUDTCalled(myName)
If Not thisPerson.Success Then
Err.Raise 19999
End If
MsgBox myName & " is a " & " is a " & thisPerson.Age & " year old " & thisPerson.Gender
teardown:
Exit Function
errhandler:
If Err.Number = 19999 Then Err.Description = myName & "is an unknown name"
MsgBox Err.Number & ", " & Err.Description
Resume teardown
End Function
Private Function MultiplesUDTCalled( _
ByVal Name As String) As Person
MultiplesUDTCalled.Success = True
Select Case Name
Case "John"
MultiplesUDTCalled.Gender = "bloke"
MultiplesUDTCalled.Age = 45
Case "Jane"
MultiplesUDTCalled.Gender = "woman"
MultiplesUDTCalled.Age = 36
Case Else
MultiplesUDTCalled.Success = False
End Select
End Function
Figure 3 – Using a UDT as a Function Type to Return Multiple Values
Passing UDT as an Argument
The fourth and final method uses a UDT as a function argument. The same considerations apply as when using a UDT as a function type. Figure 4 shows an example of returning multiple values using a UDT as a function argument.
Public Type Person
Name As String
Gender As String
Age As Long
Success As Boolean
End Type
Public Function MultiplesUDTCaller()
Dim myName As String
Dim thisPerson As Person
Dim isBlokeWoman As String
On Error GoTo errhandler:
thisPerson.Name = "John"
If Not MultiplesUDTCalled(thisPerson) Then
Err.Raise 19999
End If
MsgBox thisPerson.Name & " is a " & " is a " & thisPerson.Age & " year old " & thisPerson.Gender
thisPerson.Name = "Jane"
If Not MultiplesUDTCalled(thisPerson) Then
Err.Raise 19999
End If
MsgBox thisPerson.Name & " is a " & " is a " & thisPerson.Age & " year old " & thisPerson.Gender
thisPerson.Name = "Damien"
If Not MultiplesUDTCalled(thisPerson) Then
Err.Raise 19999
End If
MsgBox thisPerson.Name & " is a " & " is a " & thisPerson.Age & " year old " & thisPerson.Gender
teardown:
Exit Function
errhandler:
If Err.Number = 19999 Then Err.Description = thisPerson.Name & "is an unknown name"
MsgBox Err.Number & ", " & Err.Description
Resume teardown
End Function
Private Function MultiplesUDTCalled( _
ByRef Them As Person) As Boolean
MultiplesUDTCalled = True
Select Case Them.Name
Case "John"
Them.Gender = "bloke"
Them.Age = 45
Case "Jane"
Them.Gender = "woman"
Them.Age = 36
Case Else
MultiplesUDTCalled = False
End Select
End Function
Figure 4 – Using a UDT as a Function Argument to Return Multiple Values
Summary
so there we have it, 4 ways to get multiple values from a procedure. ALl work, so it is a matter of preference or suitability as o which to use. Personally, I don’t use UDTs, my preference is for multiple arguments within a function. Of curse I use classes, but not for this being able to return multiple values, but in situations where a class suits my application design.
As an aside, I don’t use subs, I always use functions. All procedures should always return at least one value, a success or failure value to pass back to the error handler. Using the function return value to pass back a succes indicator does mean that where you do need that function to return some value determined within the function, just think of any type of calculator, the function return value has been used up, so you will necessarily need to pass back multiple values.
