# Vectors of Unions between concrete type and singleton type
**URL:** https://discourse.julialang.org/t/vectors-of-unions-between-concrete-type-and-singleton-type/101158
**Category:** General Usage
**Created:** [July 4, 2023, 9:23am UTC](https://discourse.julialang.org/t/vectors-of-unions-between-concrete-type-and-singleton-type/101158 "2023-07-04T09:23:55Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@hexaeder](https://discourse.julialang.org/u/hexaeder)
#### Post date: [July 4, 2023, 9:23am UTC](https://discourse.julialang.org/t/vectors-of-unions-between-concrete-type-and-singleton-type/101158/1 "2023-07-04T09:23:55Z")
According to [the docs](https://docs.julialang.org/en/v1/manual/missing/#Arrays-With-Missing-Values), `Vector{Union{Missing, <:Any}}` can be fast fast because they use a special memory layout to mark “missing” fields.
Is that special handling for `missing`, or is it true for Arrays of all singleton unions, such as `Union{Nothing, <:Any}` or `Union{Makie.Automatic, <:Any}`?
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### Author:  [@jling](https://discourse.julialang.org/u/jling)
#### Post date: [July 4, 2023, 9:36am UTC](https://discourse.julialang.org/t/vectors-of-unions-between-concrete-type-and-singleton-type/101158/2 "2023-07-04T09:36:27Z")
Any ruins everything, nothing is gonna be fast if you have abstract type in array
But otherwise, it’s true for all singletom
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### Author:  [@hexaeder](https://discourse.julialang.org/u/hexaeder)
#### Post date: [July 4, 2023, 9:38am UTC](https://discourse.julialang.org/t/vectors-of-unions-between-concrete-type-and-singleton-type/101158/3 "2023-07-04T09:38:42Z")
By writing `Union{Missing, <:Any}` I meant that the second type in the Union is a concrete subtype and bitstype, similar to the Missing case.
> But otherwise, it’s true for all singletom
okay, thanks!