Again about reference and sub parameter passing

[acorrias]

Hi
I'm discovering b4a languages features in order to get a large know how. I have two questions:
a) is it possibile to pass an whole array to a sub?

thats to say
dim a(9) as int
.
sub grind_array (x....) <<<<??? how to specify formal parameter???
x(5)=4
end sub

I have tryed to code the following code but I get an error "Use of undeclared array: x"

Sub Globals
   Dim b(10), i As Int
   For i=0 To 9 :    b(i)=i*i : Next
   Log("actual param before: "& b(5)) 'Prints b(5) before sub call
    S2(b)
    Log("actual param after: " & b(5)) 'Prints b(5) after sub call
End Sub

Sub S2(x As Object)
   Log("formal param before: "& x) 'Prints x 
   x(5)=666
    Log("formal param after: " &x) 'Prints x
End Sub

b) I read the Erel's post about Variables & Objects in Basic4android. I'm studying about the phrase "When you pass a non-primitive to a sub or when you assign it to a different variable, a copy of the reference is passed." and about "All types can be treated as Objects". So I tryed another example passing the single array cell but it seems that it's behaving as value passing. let's see.

Sub Globals
   Dim b(10), i As Int
   For i=0 To 9 :    b(i)=i*i : Next
   Log("actual param before: "& b(5)) 'Prints b(5) before sub call
    S2(b(5))
    Log("actual param after: " & b(5)) 'Prints b(5) after sub call
End Sub

Sub S2(x As Int)
   Log("formal param before: "& x) 'Prints x 
   x=666
    Log("formal param after: " & x) 'Prints x
End Sub

I thought that the correct value for the actual param after the s2 call would be 666 and not 25.

So, could you help me understanding this topic.

cheers
alex

 

[Erel]

a) Yes.

Dim x(10) As Int
Dim y(20, 30) As Int
Dim z() As Button

z = s1 (x, y)

Sub s1 (x() As Int, y(,) As Int) As Button()
 For i = 0 To x.Length - 1
  Log(x(i))
 Next
...
End Sub

b) The type of a specific element in your array is Int, which is a primitive type. The element is passed by value in this case.
Try this code:

Dim b(1) As Int
b(0) = 25

S1(b)
Log(b(0)) '666

...

Sub S1 (x() As Int)
 x(0) = 666
End Sub