# Concrete types for Dicts in container

**URL:** <https://discourse.julialang.org/t/concrete-types-for-dicts-in-container/28043>\
**Category:** General Usage\
**Created:** [August 27, 2019, 2:03pm UTC](https://discourse.julialang.org/t/concrete-types-for-dicts-in-container/28043 "2019-08-27T14:03:12Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![mrVeng](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mrveng/32/8836_2.png) [@mrVeng](https://discourse.julialang.org/u/mrVeng)\
**Post date:** [August 27, 2019, 2:03pm UTC](https://discourse.julialang.org/t/concrete-types-for-dicts-in-container/28043/1 "2019-08-27T14:03:13Z")

</div>

Hi everyone!

I am trying to construct a container that holds vectors of different probabilities (but they are all either multi- or univariate). This container is used to store prior distributions of parameter I use in another struct, so one of the fields is a Dict that maps symbols to Vectors of distributions. The following could be used for a concrete type definition:

```julia
using Distributions
using BenchmarkTools

#3 - Issue for concrete types
typeof( [Normal(), Normal()] ) #Vector{Normal{Float64}}
typeof( [Gamma(1,2), Normal()] ) #Vector{Distribution{Univariate, Continuous}}
typeof( [Normal(), Normal()] ) <: Vector{<:Distribution{Univariate} } #true
typeof( [Gamma(1,2), Normal()] ) <: Vector{<:Distribution{Univariate} } #true
typeof( [Poisson(1), Normal()] ) <: Vector{<:Distribution{Univariate} } #true

#all combinations above are subtype of Vector{<:Distribution{Univariate} }
Dict(:μ => [Normal(1,2), Normal(3,4)],
     :δ => [Gamma(1,1), Exponential(1)] ) #Dict Symbol -> Array{T,1} where T
#but somehow here no concrete type is assigned

```

So as a first guess I would assign the following container:

```julia
struct Prior01{A<:VariateForm}
    α :: Dict{Symbol, Vector{<:Distribution{A}} }
end
# Concretely typed not working
p01 = Prior01( Dict(:μ => [Normal(1,2), Gamma(3,4)],
             :δ => [Gamma(1,1), Gamma(1,1)] ) )

```

For some reasons I do not understand, this is not working - so a non-concretely typed version so far is the best I could do:

```julia
struct Prior02
    α :: Dict{Symbol, <:Vector{C} where {C} }
end

#Working but no concrete type
p02 = Prior02( Dict(:μ => [Gamma(1,2), Gamma(3,4)],
             :δ => [Gamma(1,1), Gamma(1,1)] ) )

```

**Question: Does anyone know why I cannot get the concretely typed container working even though the Vectors of Distributions shown above have a common supertype?**

Best regards,

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<div class="post-metadata">

**Author:** ![Vasily\_Pisarev](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/vasily_pisarev/32/7929_2.png) [@Vasily\_Pisarev](https://discourse.julialang.org/u/Vasily_Pisarev)\
**Post date:** [August 27, 2019, 9:24pm UTC](https://discourse.julialang.org/t/concrete-types-for-dicts-in-container/28043/2 "2019-08-27T21:24:24Z")

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Does `eltype()` return the same for `[Gamma(1,2), Gamma(3,4)]` and `[Gamma(1,1), Gamma(1,1)]`? If not, then their closest common supertype is indeed `Vector{<:Any}`.  
If you want to have `Vector{Distribution}` as the value type for the dictionary, then use it explicitly when calling the constructor:

```julia
p02 = Prior02( Dict{Symbol, Vector{Distribution}}(:μ => [Normal(1,2), Gamma(3,4)],
             :δ => [Gamma(1,1), Gamma(1,1)] ) )

```

Note, however, that `Vector{Distribution}` isn’t a concrete type, so you still get boxing there. But that still provides a hint to the type inference system.

---

<div class="post-metadata">

**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [August 28, 2019, 5:54am UTC](https://discourse.julialang.org/t/concrete-types-for-dicts-in-container/28043/3 "2019-08-28T05:54:29Z")

</div>

> [@Vasily\_Pisarev](#):
>
> But that still provides a hint to the type inference system.

I don’t think this matters in practice. For the compiler, it is commonly just best to bail to `Any` for non-concrete types.

---

<div class="post-metadata">

**Author:** ![mrVeng](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mrveng/32/8836_2.png) [@mrVeng](https://discourse.julialang.org/u/mrVeng)\
**Post date:** [August 28, 2019, 9:46am UTC](https://discourse.julialang.org/t/concrete-types-for-dicts-in-container/28043/4 "2019-08-28T09:46:42Z")

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> [@Vasily\_Pisarev](#):
>
> `eltype()` return the same for `[Gamma(1,2), Gamma(3,4)]` and `[Gamma(1,1), Gamma(1,1)]` ?

Thank you for your answer! `eltype()`does return the same for  
`[Gamma(1,2), Gamma(3,4)]` and `[Gamma(1,1), Gamma(1,1)]`, but not for  
`[Normal(1,2), Gamma(3,4)]` and `[Gamma(1,1), Gamma(1,1)]`,  
which I think you might have meant?

In that case, I will have to resort to `Any`then, as you two suggested.