# Clarifications regarding the Arena Allocator

**URL:** <https://ziggit.dev/t/clarifications-regarding-the-arena-allocator/17647>\
**Category:** Help\
**Tags:** language\
**Created:** [September 18, 2026, 9:52pm UTC](https://ziggit.dev/t/clarifications-regarding-the-arena-allocator/17647 "2026-09-18T21:52:31Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![vic1500](https://ziggit.dev/user_avatar/ziggit.dev/vic1500/32/9702_2.png) [@vic1500](https://ziggit.dev/u/vic1500)\
**Post date:** [September 18, 2026, 9:52pm UTC](https://ziggit.dev/t/clarifications-regarding-the-arena-allocator/17647/1 "2026-09-18T21:52:31Z")

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Hello, so let’s say I happen to create 3 array list to do something in my program. Now, I don’t wanna have to defer `ArrayList.deini()` for each 3. So I decide to use an `Arena Allocator` and use that allocator for the 3 lists. Would just calling `Arena.deinit()` guarantee that the memory for all 3 of my ArrayList is freed? Or is it possible that moemory would be leaked and nothing would be picked up because `Arena.deinit()` was called?

Thank you 🫠

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**Author:** ![pasta](https://ziggit.dev/user_avatar/ziggit.dev/pasta/32/6273_2.png) [@pasta](https://ziggit.dev/u/pasta)\
**Post date:** [September 18, 2026, 10:01pm UTC](https://ziggit.dev/t/clarifications-regarding-the-arena-allocator/17647/2 "2026-09-18T22:01:04Z")

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Yes, if you’re giving the arraylists the arena’s `allocator()`, you only need to deinit the arena.

Top tip - tests will detect leaks, so you can check this yourself!

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**Author:** ![vic1500](https://ziggit.dev/user_avatar/ziggit.dev/vic1500/32/9702_2.png) [@vic1500](https://ziggit.dev/u/vic1500)\
**Post date:** [September 18, 2026, 10:01pm UTC](https://ziggit.dev/t/clarifications-regarding-the-arena-allocator/17647/3 "2026-09-18T22:01:34Z")

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Alright… Thank you very much

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**Author:** ![Sze](https://ziggit.dev/user_avatar/ziggit.dev/sze/32/496_2.png) [@Sze](https://ziggit.dev/u/Sze)\
**Post date:** [September 19, 2026, 12:52am UTC](https://ziggit.dev/t/clarifications-regarding-the-arena-allocator/17647/4 "2026-09-19T00:52:58Z")

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Just be aware that using growing (and thus re-allocating) data structures with arenas can cause a lot of fragmentation and unusable memory space within the arena, it depends on your usage patterns and how and when those data structures grow / are resized.

If the arena is short lived this may not matter for your program.

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**Author:** ![vic1500](https://ziggit.dev/user_avatar/ziggit.dev/vic1500/32/9702_2.png) [@vic1500](https://ziggit.dev/u/vic1500)\
**Post date:** [September 19, 2026, 1:03am UTC](https://ziggit.dev/t/clarifications-regarding-the-arena-allocator/17647/5 "2026-09-19T01:03:34Z")

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Oh okay then. Noted. Thank you