Nachtrag
Ich habe mal bei Andrew Pitonyak nachgeforscht zum Thema "Optional"
und "IsMissing":
[1] Nach einem optionalen Parameter dürfen nur noch optionale
Parameter folgen.
[2] Man kann jeden optionalen Parameter weglassen, auch, wenn auf
diesen ein Komma folgt, aber:
BEZUG 1: Das funktioniert nur, wenn die optionalen Parameter vom Typ
"Variant" sind.
BEZUG 2: Pitonyak hat dieses Verhalten als BUG (der
"IsMissing"-Anweisung) eingestuft und gemeldet.
BEZUG 3: Apache OpenOffice (AOO) Bugzilla fühlt sich nicht
zuständig, weil es nichts mit StarBasic zu tun hat.
[3] Das Beispiel in der "LO BASIC-IDE Hilfe" zu "Optional" ist
fehlerfrei (BEZUG 4):
+ Es entspricht BEZUG 1.
+ Allerdings wäre es hilfreich, wenn darauf hingewiesen würde, dass
auf Grund eines noch bestehenden BUGs nur genau diese Variante
(bezüglich der Typ-Deklarationen) funktioniert.
[4] Auf Grund des noch bestehenden BUGs (wenn denn Pitonyak mit seiner
Einschätzung richtig liegt) tendiere ich persönlich zu Thomas'
Vorschlag "sauberer Programmierung" (keinen optionalen Parameter
zwischen zwei Kommas weglassen), da man zu leicht vergessen könnte,
dass eine (in allen Nutzungs-Varianten) funktionierende
"IsMissing"-Anweisung zwingend von der Typ-Deklaration "Variant"
abhängt für alle optionalen Parameter.
Grüße
Hans-Werner
BEZUG 1: Andrew Pitonyak (04.2016 - S.55/56) -
http://www.pitonyak.org/OOME_3_0.odt
Optional arguments
You can declare arguments as optional by preceding them with the
keyword Optional. All of the arguments following an optional argument
must also be optional. Use the IsMissing function to determine if an
optional argument is missing.
Listing 30. Optional arguments.
REM Make test calls with optional arguments.
REM Calls with Integer and Variant arguments should yield the same
result.
REM Unfortunately, they do not.
Sub ExampleArgOptional()
Dim s$
s = "Variant Arguments () => " & TestOpt() & CHR$(10) &_
"Integer Arguments () => " & TestOptI() & CHR$(10) &_
"---------------------------------------------" & CHR$(10) &_
"Variant Arguments (,,) => " & TestOpt(,,) & CHR$(10) &_
"Integer Arguments (,,) => " & TestOptI(,,) & CHR$(10) &_
"---------------------------------------------" & CHR$(10) &_
"Variant Arguments (1) => " & TestOpt(1) & CHR$(10) &_
"Integer Arguments (1) => " & TestOptI(1) & CHR$(10) &_
"---------------------------------------------" & CHR$(10) &_
"Variant Arguments (,2) => " & TestOpt(,2) & CHR$(10) &_
"Integer Arguments (,2) => " & TestOptI(,2) & CHR$(10) &_
"---------------------------------------------" & CHR$(10) &_
"Variant Arguments (1,2) => " & TestOpt(1,2) & CHR$(10) &_
"Integer Arguments (1,2) => " & TestOptI(1,2) & CHR$(10) &_
"---------------------------------------------" & CHR$(10) &_
"Variant Arguments (1,,3) => " & TestOpt(1,,3) & CHR$(10) &_
"Integer Arguments (1,,3) => " & TestOptI(1,,3) & CHR$(10)
MsgBox s, 0, "Optional Arguments of Type Variant or Integer"
End Sub
REM Return a string that contains each argument. If the argument
REM is missing, then an M is used in its place.
Function TestOpt(Optional v1, Optional v2, Optional v3) As String
TestOpt = "" & IIF(IsMissing(v1), "M", Str(v1)) &_
IIF(IsMissing(v2), "M", Str(v2)) &_
IIF(IsMissing(v3), "M", Str(v3))
End Function
REM Return a string that contains each argument. If the argument
REM is missing, then an M is used in its place.
Function TestOptI(Optional i1%, Optional i2%, Optional i3%) As String
TestOptI = "" & IIF(IsMissing(i1), "M", Str(i1)) &_
IIF(IsMissing(i2), "M", Str(i2)) &_
IIF(IsMissing(i3), "M", Str(i3))
End Function
You can omit any optional arguments. Listing 30 demonstrates two
functions that accept optional arguments. The functions are the same
except for the argument types. Each function returns a string
containing the argument values concatenated together. Missing
arguments are represented by the letter “M” in the string. Although
the return values from TestOpt and TestOpt1 should be the same for the
same argument lists, they are not (see Figure 27). This is a bug.
TIP: The IsMissing function returns incorrect results for variables
that are not of type Variant when the missing argument is followed by
a comma.
Variant Arguments () => MMM
Integer Arguments () => MMM
---------------------------------------------
Variant Arguments (,,) => MMM
Integer Arguments (,,) => 448 448M
---------------------------------------------
Variant Arguments (1) => 1MM
Integer Arguments (1) => 1MM
---------------------------------------------
Variant Arguments (,2) => M 2M
Integer Arguments (,2) => 448 2M
---------------------------------------------
Variant Arguments (1,2) => 1 2M
Integer Arguments (1,2) => 1 2M
---------------------------------------------
Variant Arguments (1,,3) => 1M 3
Integer Arguments (1,,3) => 1 448 3
Figure 27. In rare cases, non-Variant optional arguments fail.
BEZUG 2: Andrew Pitonyak (06.2015 - S.399) -
http://www.pitonyak.org/AndrewMacro.odt
Warning
As of version 1.0.3.1, IsMissing will fail with Optional parameters if
the type is not Variant and the missing optional parameter is
represented by two consecutive commas. I first investigated this
behavior after speaking with Christian Anderson [ca@ofs.no]. This is
issue 11678 in issuezilla.
BEZUG 3: https://bz.apache.org/ooo/show_bug.cgi?id=11678
Unknown 2003-02-25 13:43:18 UTC
Misfiled, the framewwork/ scripting deals with the langauge
independent scripting framework, not Star Basic:
BEZUG 4: Test-Makros
Sub Calling_VARIANT
Dim A,B,C as String
A = "A" : B = "B" : C = "C" : D = "D"
Called_VARIANT(A,,,D)
End Sub
Sub Called_VARIANT(Optional AA as Variant,Optional BB as
Variant,Optional CC as Variant)
MsgBox("IsMissing(AA)=" & IsMissing(AA) & Chr(13) &_
"IsMissing(BB)=" & IsMissing(BB) & Chr(13) &_
"IsMissing(CC)=" & IsMissing(CC) & Chr(13) &_
"IsMissing(CC)=" & IsMissing(DD) & Chr(13))
End Sub
MsgBox-Ausgabe:
IsMissing(AA)=False
IsMissing(BB)=True
IsMissing(CC)=True
IsMissing(CC)=False
----------------------------------------------------------------------------------------
Sub Calling_INTEGER
Dim A,B,C as Integer
A = 1 : B = 2 : C = 3 : D = 4
Called_INTEGER(A,,,C)
End Sub
Sub Called_INTEGER(Optional AA as Integer,Optional BB as
Integer,Optional CC as Integer)
MsgBox("IsMissing(AA)=" & IsMissing(AA) & Chr(13) &_
"IsMissing(BB)=" & IsMissing(BB) & Chr(13) &_
"IsMissing(CC)=" & IsMissing(CC) & Chr(13) &_
"IsMissing(CC)=" & IsMissing(DD) & Chr(13))
End Sub
MsgBox-Ausgabe:
IsMissing(AA)=False
IsMissing(BB)=False
IsMissing(CC)=False
IsMissing(CC)=False