# What are the DataType and Union definitions?

**URL:** <https://discourse.julialang.org/t/what-are-the-datatype-and-union-definitions/4332>\
**Category:** General Usage\
**Created:** [June 17, 2017, 11:04pm UTC](https://discourse.julialang.org/t/what-are-the-datatype-and-union-definitions/4332 "2017-06-17T23:04:58Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![hpoit](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/hpoit/32/245_2.png) [@hpoit](https://discourse.julialang.org/u/hpoit)\
**Post date:** [June 17, 2017, 11:04pm UTC](https://discourse.julialang.org/t/what-are-the-datatype-and-union-definitions/4332/1 "2017-06-17T23:04:58Z")

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```julia
typeof(Union{Real,Rational}) # => DataType
typeof(Union{Real,String}) # => Union (1)
typeof(Union{Real,Float64}) # => DataType
typeof(Union{Int64,Float64}) # => Union (2)
typeof(Union{Real,Float64,Rational}) # => DataType
typeof(Union{Real,AbstractFloat,Rational}) # => DataType

```

DataType and Union definitions are not clear to me. Help is appreciated!

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**Author:** ![yuyichao](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yuyichao/32/20_2.png) [@yuyichao](https://discourse.julialang.org/u/yuyichao)\
**Post date:** [June 17, 2017, 11:18pm UTC](https://discourse.julialang.org/t/what-are-the-datatype-and-union-definitions/4332/2 "2017-06-17T23:18:18Z")

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> [@hpoit](#):
>
> typeof(Union{Real,Rational}) # =\> DataType  
> typeof(Union{Real,String}) # =\> Union (1)  
> typeof(Union{Real,Float64}) # =\> DataType  
> typeof(Union{Int64,Float64}) # =\> Union (2)  
> typeof(Union{Real,Float64,Rational}) # =\> DataType  
> typeof(Union{Real,AbstractFloat,Rational}) # =\> DataType

```julia
julia> Union{Real,Rational}
Real

julia> Union{Real,String}
Union{Real, String}

julia> Union{Real,Float64}
Real

julia> Union{Int64,Float64}
Union{Float64, Int64}

julia> Union{Real,Float64,Rational}
Real

julia> Union{Real,AbstractFloat,Rational}
Real

```

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**Author:** ![yuyichao](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yuyichao/32/20_2.png) [@yuyichao](https://discourse.julialang.org/u/yuyichao)\
**Post date:** [June 18, 2017, 12:42am UTC](https://discourse.julialang.org/t/what-are-the-datatype-and-union-definitions/4332/3 "2017-06-18T00:42:43Z")

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I’ll add that if the code shown above doesn’t answer your question, you need to be more specific about what your confusion is…