Parameters extensions

Parameters with default values specified

As you know in VFP all the parameters declared with LPARAMETERS are by default optional so the following code is valid

SomeProcedure()
SomeProcedure("test")
SomeProcedure("test",1)

PROCEDURE SomeProcedure
LPARAMETERS tcValue, tnvalue, teValue

And the parameters not passed are intialized to .F.

When using the TPARAMETERS syntax, you need to pass all the parameters declared otherwise you get a compile time VFPCE0017 error about not overload with the matching parameters was found:.

SomeInfo("") && Show VFPCE0017
SomeInfo("",1) && Show VFPCE0017

PROCEDURE SomeInfo
TPARAMETERS tcValue as string, tnValue as integer, teValue 

	

Now you can declare what will be the default value for your parameters so:

SomeInfo()
SomeInfo("") 
SomeInfo("",1) 

PROCEDURE SomeInfo
TPARAMETERS tcValue as string = "", tnValue as integer = -1, teValue = NULL

				

And the compiler generates the following code:

  SomeInfo("", -1, null)      
  SomeInfo("", -1, null)      
  SomeInfo("", 1, null)  

The same applies to typical PROCEDUREs with parameters declared with LPARAMETERS. In that case you can also use PCOUNT() to figure out how may parameters were passed to the procedure.

PROCEDURE SomeProcedure
LPARAMETERS tcValue = "test", tnvalue = 0, teValue  && teValue defaults to .F. the other to the expression

Variable number of Arguments in procedures (VarArgs / unbound number of parameters)

Sometimes you need to have a procedure that can receive from 0 to n parameters, and you may not know what would be the upper bound for n. The compiler allows you to define procedures with variable number of parameters, known in the c / Java languages as varargs. You declare a procedure like that with:

PROCEDURE SumSquares
TPARAMETERS eValues() as double ...
LOCAL i, nResult
nResult = 0
FOR i = 0 TO ALEN(eValues)-1  && Start in zero because in .NET ParamArrays are zero based
	nResult = m.nResult + eValues(m.i)^2
ENDFOR
RETURN m.nResult                

And you invoke it with:

IF  SumSquares(1,2,3,4,5,6) != 91
	ERROR "ParamArray sum is failing"
ENDIF

The parameter that is varargs is declared as varargs using the three DOTS (.) after the parameter declaration Also the parameter must be the last one appearing in the TPARAMETERS declaration.

You can include other parameters before the varargs parameter as here:

PROCEDURE ComputeQubic
TPARAMETERS tnX, eValues()  ...