# How do these Union{Missing, T}s differ in practice?

**URL:** <https://discourse.julialang.org/t/how-do-these-union-missing-t-s-differ-in-practice/8464>\
**Category:** General Usage\
**Created:** [January 18, 2018, 11:22pm UTC](https://discourse.julialang.org/t/how-do-these-union-missing-t-s-differ-in-practice/8464 "2018-01-18T23:22:55Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![JeffreySarnoff](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jeffreysarnoff/32/1980_2.png) [@JeffreySarnoff](https://discourse.julialang.org/u/JeffreySarnoff)\
**Post date:** [January 18, 2018, 11:22pm UTC](https://discourse.julialang.org/t/how-do-these-union-missing-t-s-differ-in-practice/8464/1 "2018-01-18T23:22:55Z")

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```julia
const MaybeReal = Union{Missing, Real}
const RealMaybe = Union{Missing, T} where T<:Real

```

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**Author:** ![bkamins](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/bkamins/32/208538_2.png) [@bkamins](https://discourse.julialang.org/u/bkamins)\
**Post date:** [January 19, 2018, 12:01am UTC](https://discourse.julialang.org/t/how-do-these-union-missing-t-s-differ-in-practice/8464/2 "2018-01-19T00:01:41Z")

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The difference is that you can write `RealMaybe{Int}`.

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<div class="post-metadata">

**Author:** ![JeffreySarnoff](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jeffreysarnoff/32/1980_2.png) [@JeffreySarnoff](https://discourse.julialang.org/u/JeffreySarnoff)\
**Post date:** [January 19, 2018, 6:56am UTC](https://discourse.julialang.org/t/how-do-these-union-missing-t-s-differ-in-practice/8464/3 "2018-01-19T06:56:44Z")

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and it knows how to specialize itself … thanks