Is variable value kept after For.. in ... do loop?

[David Heffernan 2345]

1 hour ago, Mike Torrettinni said:

I was referring to variable iterating For..in loop - in this case full array record content is copied into variable. No? At least that's what I see from the simple example above.

Yes that is correct. My argument stands.

 

Copying the full record into a local is only expensive (compared to reading a value from the record in-situ in the array) if the record is large.  For a small record, copying a handful of bytes costs no more than reading even a single byte.

 

I'm arguing against your claim that there would be a performance hit using a for in loop even for small records.  For large records there will be a hit.  Not for small records.

Edited September 24, 2020 by David Heffernan

[Stefan Glienke 2002]

Pointer shifting over an array might only be faster because the array variable itself needs to be accessed again every time - this is mostly the case when the array itself is a field in a class and you are inside of a method. Accessing say FItems[LIndex] in a loop causes access to Self.FItems all the time. Simple storing @FItems[0] in a local variable and Inc that might be faster - but only because you then have avoided the array field access, not because pointer is faster than indexing into an array.

 

Edit: even more so if you access that FItems[LIndex] multiple times - the compiler most of the time generates code to fetch FItems each and every time and does not treat it as if you stored it inside a temporary variable.

Edited September 24, 2020 by Stefan Glienke

[David Heffernan 2345]

REMOVED, sorry, was dupe
 

Edited September 24, 2020 by David Heffernan

[Mike Torrettinni 198]

1 minute ago, David Heffernan said:

Yes, we've agreed on that. The thing is that's only a performance issue (compared to direct access of the record in-situ in the array) if the record is large.  Because if the record is small, then copying a handful of bytes costs the same as reading even a single byte.

 

Yes. I have a situaition where initial simple structure has become quite extended with nested records. So, what seemed at the beginning a very elegant solution with For..in, is now becoming a little slower due to more complex structure and more extensive use. and I don't want to risk this to be performance hog for large customers (high number of records).

 

I have decided to stop using For..in, so when I code I don't need to think about it. Now I have good reason to stick with 1 style.

Except if I will open source anything, that's when I see a For..in looks much better.