# Help with understanding Julia types

**URL:** <https://discourse.julialang.org/t/help-with-understanding-julia-types/86345>\
**Category:** New to Julia\
**Created:** [August 25, 2022, 4:36pm UTC](https://discourse.julialang.org/t/help-with-understanding-julia-types/86345 "2022-08-25T16:36:18Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![akshdfyehd](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/akshdfyehd/32/39097_2.png) [@akshdfyehd](https://discourse.julialang.org/u/akshdfyehd)\
**Post date:** [August 25, 2022, 4:36pm UTC](https://discourse.julialang.org/t/help-with-understanding-julia-types/86345/1 "2022-08-25T16:36:18Z")

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Hi, I am relatively new to Julia, can you explain what difference between Union {Missing,T}, Vector{Bool}, [Union{Missing, Bool} are, please? Thanks!

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**Author:** ![mkitti](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mkitti/32/12459_2.png) [@mkitti](https://discourse.julialang.org/u/mkitti)\
**Post date:** [August 25, 2022, 4:54pm UTC](https://discourse.julialang.org/t/help-with-understanding-julia-types/86345/2 "2022-08-25T16:54:46Z")

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`Union{Missing, Bool}` is a sum type union between `Missing` and `Bool`. That is the value can be either of type `Missing` or of type `Bool`.

`Vector{Union{Missing, Bool}}` is a 1-D array where the elements could be either of type `Missing` or of `Bool`.

`Union{Missing, Bool}[true, false, missing]` is a literal syntax to create a `Vector{Union{Missing, Bool}}`.

```julia
julia> A = Union{Missing, Bool}[true, false, missing]
3-element Vector{Union{Missing, Bool}}:
  true
 false
      missing

julia> typeof(A)
Vector{Union{Missing, Bool}} (alias for Array{Union{Missing, Bool}, 1})

```

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<div class="post-metadata">

**Author:** ![akshdfyehd](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/akshdfyehd/32/39097_2.png) [@akshdfyehd](https://discourse.julialang.org/u/akshdfyehd)\
**Post date:** [August 25, 2022, 5:20pm UTC](https://discourse.julialang.org/t/help-with-understanding-julia-types/86345/3 "2022-08-25T17:20:44Z")

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Thank you so much!!!