cat • methoddecl

Method Declaration

Procedures

[ FAST [ UNSAFE] ] [ STATIC ] { PUBLIC | PRIVATE } { PROCEDURE | SUB } Identifier ( [ [ BYREF ] Parameter AS Datatype [ , … ] ] [ , ] [ OPTIONAL [ BYREF ] Optional Parameter AS Datatype [ , … ] ] [ , ] [ ... ] ) ... END

This declares a procedure, i.e. a method that returns nothing.

The END keyword indicates the end of the procedure.

Functions

[ FAST [ UNSAFE] ] [ STATIC ] { PUBLIC | PRIVATE } { FUNCTION | PROCEDURE | SUB } Identifier ( [ [ BYREF ] Parameter AS Datatype [ , … ] ] [ , ] [ OPTIONAL [ BYREF ] Optional Parameter AS Datatype [ , … ] ] [ , ] [ ... ] ) AS Datatype ... END

This declares a function, i.e. a method that returns a value.

The END keyword indicates the end of the function.

The datatype of the return value must be specified.

These declarations must be written on a unique line. They are separated here so that the syntax is readable.

Returning a value from a function

Use the RETURN keyword to terminate the function and pass the return value back to the caller.

Example

Public Sub Main()
  Print Calc(0);; Calc(0.5);; Calc(1)
End
 
Function Calc(fX As Float) As Float
  Return Sin(fX) * Exp(- fX)
End
0 0.290786288213 0.309559875653

Method Access

The method is accessible everywhere in the class it is declared.

  • If the PUBLIC keyword is specified, it is also accessible to the other classes having a reference to an object of this class.

  • If the STATIC keyword is specified, the method can only access to the static variables of the class.

Method Arguments

All method arguments are separated by commas.

  • If the OPTIONAL keyword is specified, all parameters after the keywords are optional. You can specify a default value after the parameter declaration by using the equal sign.

Example

STATIC PUBLIC PROCEDURE Main()
...
PUBLIC FUNCTION Calc(fA AS Float, fB AS Float) AS Float
...
PRIVATE SUB DoIt(sCommand AS String, OPTIONAL bSaveIt AS Boolean = TRUE)
...
STATIC PRIVATE FUNCTION MyPrintf(sFormat AS String, ...) AS Integer
  • If the parameters list end with ..., then the method can take extra arguments. Every additional argument passed to the method is accessible with the Param class.

Passing extra arguments with "..."

Since 3.6

We can either pass a known number of arguments through Function1() to Function2() using the ... keyword
or it can be used as a variadic expression using the Param class to pass any number of any datatype.

The ... keyword is used to transmit all the extra arguments to the function accepting them.

Example 1

Passing a known number of arguments to another function.

Sub Main()

  PassSomeArgs("warning", "format description" , "info")
  
End


Sub PassSomeArgs(sType As String, ...)

  ' Do something with sType and pass all the other args to the next function.

  Print "Got message type " & sType

  PrintMessage(sType, ...)

End

Sub PrintMessage(sType as String, sFormat as String, sInfo as String)

  ' Do some stuff with the known number of arguments passed.

End

Example 2

Using Param class to pass any number of arguments of any datatype (variadic)


Sub Main()

  ProcessVariadic("warning", "format description" , "info", -1)

End

Sub ProcessVariadic(...)

' Here we use the Param class to access and print all arguments supplied via "..." (you must take care of variable types if they are unknown)

Print "There are " & Param.Count & " arguments"

 Dim iType As Integer

  For Each vVar As Variant In Param.All

  iType = TypeOf(vVar)

    If iType = gb.String then 
     Print "Arg is a String: " & vVar

    Else If iType = gb.Integer then 
     Print "Arg is Integer: " & Str(vVar)

    Endif

  Next

End

Arguments Passed By Reference

When the BYREF keyword is specified, the argument must be an assignment expression that will be modified by the called function.

Example

SUB ConvPixelToCentimeter(BYREF Value as Float, Dpi AS Integer)

  Value = Value / Dpi * 2.54

END

PUBLIC SUB Main()

  DIM Size AS Float

  Size = 256
  ConvPixelToCentimeter(BYREF Size, 96)
  PRINT Size

END
6.773333333333

The BYREF keyword must be specified both at function declaration and at function call!

If you do not specify BYREF at function call, then the argument is passed by value, even if BYREF was specified at function declaration.

In other words: the called function allows an argument to be passed by reference, whereas the caller decides it.

Just In-Time Compilation

Since 3.2

If the FAST keyword is used, then the method will be optimized by the Just In Time Compiler.

Since 3.12

Moreover, if the UNSAFE keyword is specified, the Just In Time Compiler will use unsafe but faster code.

See also