# Approaches to sentinel values in immutables

**URL:** <https://discourse.julialang.org/t/approaches-to-sentinel-values-in-immutables/129675>\
**Category:** General Usage\
**Tags:** question\
**Created:** [June 5, 2025, 5:56pm UTC](https://discourse.julialang.org/t/approaches-to-sentinel-values-in-immutables/129675 "2025-06-05T17:56:29Z")\
**Posts on this page:** 1\
**Showing post:** 15

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**Author:** ![Dan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dan/32/42581_2.png) [@Dan](https://discourse.julialang.org/u/Dan)\
**Post date:** [June 6, 2025, 2:31am UTC](https://discourse.julialang.org/t/approaches-to-sentinel-values-in-immutables/129675/15 "2025-06-06T02:31:47Z")

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Just recently this package surfaced:

> [@\[ANN\] SmallCollections.jl: fast small vectors, sets and dictionaries](https://discourse.julialang.org/t/ann-smallcollections-jl-fast-small-vectors-sets-and-dictionaries/128787):
>
> The standard container types in Julia (Vector, Set, Dict) can hold an arbitrary number of elements. If the size is known in advance, one can use dedicated types like SVector or MVector from StaticArrays.jl that are much faster and, in the case of SVector, don’t allocate any memory. In many problems, however, the size is not fixed, but instead known to be “small”. In enumerative combinatorics, for example, combinatorial explosions make it often impossible to reach “large” vectors or sets. SmallC…

The package tries to maintain the speed of `SVector` with the interface of `Vector` for small lengths. Perhaps a `SmallVector{3,Node}` will get the performance you need with nice syntax.

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