# SizedVector and Float32

**URL:** <https://discourse.julialang.org/t/sizedvector-and-float32/99003>\
**Category:** General Usage\
**Created:** [May 17, 2023, 3:45pm UTC](https://discourse.julialang.org/t/sizedvector-and-float32/99003 "2023-05-17T15:45:11Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![erlebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/erlebach/32/12973_2.png) [@erlebach](https://discourse.julialang.org/u/erlebach)\
**Post date:** [May 17, 2023, 3:45pm UTC](https://discourse.julialang.org/t/sizedvector-and-float32/99003/1 "2023-05-17T15:45:11Z")

</div>

I encountered an issue with `SizedVector` in `StaticArrays.jl`.

The following works:

```julia
i::Int64 = 3
a = SizedVector{i}([1., 2., 3.])

```

But if `i` is an `Int32`, I get an error:

```julia
j::Int32 = 3
a = SizedVector{j}([1., 2., 3.])

```

I get the error:

```julia
ERROR: TypeError: in typeassert, expected Tuple{Vararg{Union{StaticArraysCore.Dynamic, Int64}}}, got a value of type Tuple{Int32}
Stacktrace:
 [1] Size
   @ ~/.julia/packages/StaticArraysCore/U2Z1K/src/StaticArraysCore.jl:464 [inlined]
 [2] Size(s::Type{Tuple{3}})
   @ StaticArraysCore ~/.julia/packages/StaticArraysCore/U2Z1K/src/StaticArraysCore.jl:470
 [3] Size(#unused#::Type{SizedVector{3, T} where T})
   @ StaticArraysCore ~/.julia/packages/StaticArraysCore/U2Z1K/src/StaticArraysCore.jl:492
 [4] size(#unused#::Type{SizedVector{3, T} where T})
   @ StaticArrays ~/.julia/packages/StaticArrays/VLqRb/src/abstractarray.jl:4
 [5] length_match_size(#unused#::Type{SizedVector{3, T} where T}, x::Vector{Float64})
   @ StaticArrays ~/.julia/packages/StaticArrays/VLqRb/src/convert.jl:122
 [6] adapt_size(#unused#::Type{SizedVector{3, T} where T}, x::Vector{Float64})
   @ StaticArrays ~/.julia/packages/StaticArrays/VLqRb/src/convert.jl:94
 [7] construct_type(#unused#::Type{SizedVector{3, T} where T}, x::Vector{Float64})
   @ StaticArrays ~/.julia/packages/StaticArrays/VLqRb/src/convert.jl:87
 [8] (SizedVector{3, T} where T)(a::Vector{Float64})
   @ StaticArrays ~/.julia/packages/StaticArrays/VLqRb/src/SizedArray.jl:15
 [9] top-level scope
   @ REPL[36]:1

```

Question: why can’t I use `Int32` to specify the size of the `SizedVector`? This restriction is either a missed edge case or it is intentional. If it is not a missed edge case, I would like to know the rationale for this decision. Thanks.

---

<div class="post-metadata">

**Author:** ![mikmoore](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mikmoore/32/31109_2.png) [@mikmoore](https://discourse.julialang.org/u/mikmoore)\
**Post date:** [May 17, 2023, 4:19pm UTC](https://discourse.julialang.org/t/sizedvector-and-float32/99003/2 "2023-05-17T16:19:50Z")

</div>

Type parameters are only used within the compiler, so there is no intrinsic speed or memory cost to a `Int64` parameter over an `Int32`.

Further, canonicalizing the length parameter to a uniform type actually seems very important here. Unsurprisingly,

```julia-repl
julia> SizedVector{Int64(3),Float64,Vector{Float64}} === SizedVector{Int32(3),Float64,Vector{Float64}}
false

```

So, even if non-`Int` parameters were accepted and you could create the object, it might struggle to interoperate with objects that used a differently-typed type parameter. It would also miss methods for things like `LinearAlgebra.cross`, which is defined only for objects with `Size{(2::Int,)}` and `Size{(3::Int,)}`.

I think that these codebases just get much much harder to write and maintain if they allow non-canonical representations like this. If it mattered, people could eventually support this, but again these values mostly exist within the compiler so there’s little value to adding this support.

`StaticArrays.jl` is far from alone in this lack of support:

```julia-repl
julia> NTuple{Int32(3),Int}
ERROR: TypeError: in Vararg, in count, expected Int64, got a value of type Int32

```

---

<div class="post-metadata">

**Author:** ![erlebach](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/erlebach/32/12973_2.png) [@erlebach](https://discourse.julialang.org/u/erlebach)\
**Post date:** [May 17, 2023, 4:33pm UTC](https://discourse.julialang.org/t/sizedvector-and-float32/99003/3 "2023-05-17T16:33:48Z")

</div>

Thank you for this explanation. Makes complete sense.