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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

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