B4R Question Can I use Structure in B4R?

Alpandino · Sep 10, 2018

Hi,
I know I can create new Type, but now I need also to create method/function for my type. This could simplify my job.
I'd like to avoid writing a new lib for this, so I'd like to know if I can use the Structure syntax, more or less in this way:

B4X:

Public Structure Box
       Dim Length As Double
       Dim Width As Double
       Dim height As Double

       Function Volume() As Double
           Return Length * Width * height
       End Function
End Structure

Is it possible to do something similar in B4R?

Thank you

Erel · Sep 11, 2018

1. Creating a new library for this is a mistake.
2. Custom types cannot have methods.

3. You can do something like:

B4X:

Sub BoxVolume(bx As Box) As Double
 Return bx.Length * bx.Width * bx.Height
End Sub

Alpandino · Sep 11, 2018

My case is a more complicated.
In a function of my custom type I need to modify some parameters of the custom type itself.
Here an example (the actual code is more complicated, but the idea is the same):

B4X:

Sub Process_Globals
    'These global variables will be declared once when the application starts.
    'Public variables can be accessed from all modules.
    Public Serial1 As Serial
    Type Box (x As Int, y As Int, z As Int)
    Dim x, y, z As Box
  
End Sub

Private Sub AppStart
    Serial1.Initialize(115200)
    Log("AppStart")
End Sub

Sub BoxVolume(bx As Box) As Double
    Return bx.x * bx.y * bx.z
End Sub

Sub BoxEnlarge(bx As Box)
    bx.x = bx.x*2
    bx.y = bx.y*2
    bx.z = bx.z*2
End Sub

The "BoxEnlarge" Sub isn't really able to change x, y, z value, because I can't pass bx for reference.
Is it possible to achieve this without a library?

Thanks

tigrot · Sep 11, 2018

Use global variables as results.
Instead of assign result to say: bx.x=bx.x*2
Write x.x=bx.x*2 and the result is available in x.x

Erel · Sep 12, 2018

Alpandino said:
Is it possible to achieve this without a library?

As I previously wrote, a library is not relevant here.

I don't understand the problem. Why can't you call:

B4X:

BoxEnlarge(x)

?

Objects are passed by reference.

Alpandino · Sep 12, 2018

Erel said:
As I previously wrote, a library is not relevant here.

I don't understand the problem. Why can't you call:

B4X:

BoxEnlarge(x)

?

Objects are passed by reference.

Really? Object are passed by reference? I read in the beginners guide that in B4R I can't pass any for reference....

JanG · Sep 12, 2018

Yes, it works. Declare a Type with one element (your var-type). And declare a variable of this new type. Then use this "type-variable" as parameter. It is now by reference.

Erel · Sep 13, 2018

Alpandino said:
Really?

Really.

B4R Question Can I use Structure in B4R?

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