BlitzMax Pass integers by reference & function scope

PixelOutlaw · March 24, 2025, 14:33:59

Hello,

I've currently got two questions.
I see GetColor seems to be able to use references to integers in order to assign them back to the parameters.
Is this a language feature that exists only in the implementation and is not available to me?

Code: BASIC

Local r:Int
Local g:Int
Local b:Int
' GetCclor assigns INTEGER (which is not a Type) parameters by reference
' How can I write functions like this?
GetColor r, g, b

Print "R " + r + " G " + g + " B " + b

Also, it seems that BlitzMax nested functions have no notion of their parents' local variables.
It would be very nice to be able to modify several parent's local values at once.

Code: BASIC

Function main()
    Local value:Int = 0
    Local value2:Int = 0
    
    ' Why can't this "see" the variable value?
    ' It would seem BlitzMax functions have no notion of parent scope
    Function foo()
        value = 42
        value2 = 43
    End Function

    foo()
    Print value
    Print value2
End Function

In other languages which support internal functions, this seems to work fine.

Python example:

Code: BASIC

def main():
    value = 0
    
    def foo():
        nonlocal value
        value = 42
        
    foo()
    print(value)

Or Scheme:

Code: BASIC

(define (main)
  (let* ((value 0)
         (foo (lambda () (set! value 42))))
    (foo)
    (display value)))

Will print 42
Both have access to the values at the point at which the function is defined.

Henri · March 24, 2025, 15:21:32

Hi,

you can use var keyword after the parameter to pass value by reference.

Code: BASIC

SuperStrict

' the following illustrates parsing function parameters by reference

Function ReturnMultiplevalues(a:Int Var,b:Int Var,c:Int Var)
 a=10
 b=20
 c=30
 Return
End Function

Local x:Int,y:Int,z:Int

ReturnMultipleValues(x,y,z)

Print "x="+x '10
Print "y="+y '20
Print "z="+z '30

-Henri

PixelOutlaw · March 24, 2025, 15:50:26

Quote from: Henri on March 24, 2025, 15:21:32Hi,

you can use var keyword after the parameter to pass value by reference.
Code: BASIC
SuperStrict

' the following illustrates parsing function parameters by reference

Function ReturnMultiplevalues(a:Int Var,b:Int Var,c:Int Var)
 a=10
 b=20
 c=30
 Return
End Function

Local x:Int,y:Int,z:Int

ReturnMultipleValues(x,y,z)

Print "x="+x '10
Print "y="+y '20
Print "z="+z '30
-Henri

Excellent! Thank you very much.

SyntaxBomb - Indie Coders

BlitzMax Pass integers by reference & function scope

PixelOutlaw

Henri

PixelOutlaw