Android Tutorial [B4X] Optional sub parameters

This is a new feature that will be added to the B4X tools.

Optional sub parameters are parameters that are declared with a default value. If an optional parameter is omitted when the sub is called, the compiler inserts the default value.
This provides an opportunity to set reasonable defaults without restricting the flexibility of the API. Many cases where we currently have multiple similar methods could be organized better using optional parameters.

Declaring a sub with optional parameters is done by adding = [value] after each optional parameter.
A required (non-optional) parameter can't come after an optional parameter. This means that all optional parameters must be listed at the end.
The default value can be a string, number, Null or other simple expressions. In the case of default values declared in Java / OBJC libraries, expressions are not supported.

Public Sub ExecQuerySingleResult(Query As String, Args As List = Null, DefaultValue As Object = Null) As Object
'Calling:
ExecQuerySingleResult("query here")
ExecQuerySingleResult("query here", Array(args, here))
ExecQuerySingleResult("query here", Array(args, here), DefaultValueHere)

Public Sub ToString (MaxNumberOfRows As Int = 5) As String
'Calling:
ToString
ToString(10)

Declaring optional sub parameters in Java library:

    public static String BytesToString(byte[] Data, @DefaultValue("0") int StartOffset, @DefaultValue("-1")int Length,
            @DefaultValue("UTF-8") String CharSet)
  'calling:
BytesToString(b)
BytesToString(b, 0, b.Length, "CP-1252")

  public Object RunMethod(String MethodName, @DefaultValue("Null") Object[] Params)
'calling
jo.RunMethod("clear")
jo.RunMethod("clear", Null)
jo.RunMethod("clear", Array(1, 2, 3))

Note that it is always a string value. It will be parsed when the library is loaded based on the parameter type.

As this is a compile-time feature, dynamically calling subs with CallSub requires all parameters.

 

[Star-Dust]

Thanks very interesting. I have a question

Public Sub BytesToString(Data() As Byte, StartOffset As Int = 0, LengthAs as Int = -1) AsString

'Calling:
'Is it possible to call by skipping a parameter?
BytesToString("text here".GetBytes("UTF8"),,5)

other

Public Sub InsertHalloString(Source As String, StartOffset As Int = 0, OtherText as String = "Hallo") AsString

'Calling:
'Is it possible to call by skipping a parameter?
InsertHalloString(" my friend",,"Hi,")

 

[Erel]

Currently no, though it is an interesting idea...

 

[aeric]

Thanks very interesting. I have a question

Public Sub BytesToString(Data() As Byte, StartOffset As Int = 0, LengthAs as Int = -1) AsString

'Calling:
'Is it possible to call by skipping a parameter?
BytesToString("text here".GetBytes("UTF8"),,5)

other

Public Sub InsertHalloString(Source As String, StartOffset As Int = 0, OtherText as String = "Hallo") AsString

'Calling:
'Is it possible to call by skipping a parameter?
InsertHalloString(" my friend",,"Hi,")

We can pass Null.
[CODE lang="b4x" highlight="2"]Sub AppStart (Args() As String)
Dim s As String = InsertHalloString(" my friend", Null, "Hi,")
Log(s)
'StartMessageLoop
End Sub

Public Sub InsertHalloString (Source As String, StartOffset As Object = 0, OtherText As String = "Hallo") As String
Dim EndIndex As Int = IIf(IsNumber(StartOffset), StartOffset, Source.Length)
If EndIndex < 0 Or EndIndex > Source.Length Then EndIndex = Source.Length
Return $"${OtherText}${Source.SubString2(0, EndIndex)}"$
End Sub[/CODE]

 

[Star-Dust]

We can pass Null.
[CODE lang="b4x" highlight="2"]Sub AppStart (Args() As String)
Dim s As String = InsertHalloString(" my friend", Null, "Hi,")
Log(s)
'StartMessageLoop
End Sub

Public Sub InsertHalloString (Source As String, StartOffset As Object = 0, OtherText As String = "Hallo") As String
Dim EndIndex As Int = IIf(IsNumber(StartOffset), StartOffset, Source.Length)
If EndIndex < 0 Or EndIndex > Source.Length Then EndIndex = Source.Length
Return $"${OtherText}${Source.SubString2(0, EndIndex)}"$
End Sub[/CODE]

Null could be a value and be assigned to, for example, a string or a typed variable

 

[MrKim]

Thanks very interesting. I have a question

Public Sub BytesToString(Data() As Byte, StartOffset As Int = 0, LengthAs as Int = -1) AsString

'Calling:
'Is it possible to call by skipping a parameter?
BytesToString("text here".GetBytes("UTF8"),,5)

other

Public Sub InsertHalloString(Source As String, StartOffset As Int = 0, OtherText as String = "Hallo") AsString

'Calling:
'Is it possible to call by skipping a parameter?
InsertHalloString(" my friend",,"Hi,")

VBA does not allow this, I believe. If you have to put in the commas may as well add the default value.