Calling method within same method

General
1

May sound a stupid question but towards the end of a method I need the method to run again so I have just called it again (within the same method) followed by “Return”.

It works but I’m wondering whether this is the best/safest way of handling this scenario or if I need to do it another way?

2

This can lead to stack overflow conditions. I would use the Calllater method of the timer http://developer.xojo.com/xojo-core-timer$CallLater which will place the call into the event loop. A delay of 0 ms is fine.

3

controlled method recursion is an acceptable and common programming practice… you just need to insure that the recursion can and does properly unwind itself.

One common use is in traversing a directory tree

function searchtree(dir as string)
    for i=0 to dir.items.count
       if dir.items(i).isDirectory then 
          searchTree(dir.items(i))
      else
        // item is a normal file
     end if
     
    next i

end function

note : this code is for illustration only, and doesn’t work as-is

4

Or just create a Timer that calls your method and adjust the Timer.Mode within the method as needed.

Or put your method’s code into a loop and exit that loop when needed.

Or call your method at the end because recursion is exactly what you want.

Without knowing exactly what you’re trying to do, it’s hard to advise.

5

Thanks Wayne. I had not heard of that option.

Thanks, Kem and Dave.

I’m actually looping through an array item by item and processing data where I need to but theoretically the stack overflow or app freeze could still happen even with a timer or CallLater because I sometimes need to iterate over the same array index more than once to parse delimited data within it.

This could mean it gets stuck if I have programmed badly. So to avoid this perhaps I should log the array index value just parsed before the delayed timer call to a global property so the next time the method is about to be called it can make sure it doesn’t process the exact same timer call again if the array index is the same as the last time.

6

Iff you post your code, perhaps we could recommend a more efficient way.

7

as Kem said, without know more its hard to give a good answer…
but here is another template to consider

  DO
    <loop thru your stuff>
   if done then break
  LOOP

this won’t cause a stack overflow, it MIGHT become an endless loop

and “done” depends on what you are doing… basically if you detect “need to iterate over the same array index more than once to parse delimited data within it.” then DONE=FALSE … the question becomes are you sure at some point DONE=TRUE???

8

if done then EXIT. (Break does something different - you’re mixing languages again).

9

I understand but my code is way too long and complex to post and wouldn’t make sense to anyone anyway.

I just wanted to know whether it was prudent to call the same method within itself or not.

Thanks for all the advice.

10

You could also post an example of an array before and after processing. It’s up to you, but I can almost guarantee that you’ll gain something from it.

11

As Dave wrote in his post above:

When I use recursion (and I do it a lot lately) I try to find a solution which is called tail-recursion. It avoids the possible stack overflow issue (Tail call). I don’t know if the Xojo compiler implements this. I assume that the 64-bit one does “by nature”, but of course I don’t know the inner workings of Xojo’s LLVM usage.

Personally as a general rule I’d recommend to use recursion instead of loops.

12

Thanks Eli.