# Creating SVector of a single SVector{1, Float64}

**URL:** <https://discourse.julialang.org/t/creating-svector-of-a-single-svector-1-float64/96979>\
**Category:** New to Julia\
**Tags:** question, staticarrays\
**Created:** [April 2, 2023, 6:08pm UTC](https://discourse.julialang.org/t/creating-svector-of-a-single-svector-1-float64/96979 "2023-04-02T18:08:57Z")\
**Posts on this page:** 1\
**Showing post:** 3

<div class="post-metadata">

**Author:** ![aafsar](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/aafsar/32/47420_2.png) [@aafsar](https://discourse.julialang.org/u/aafsar)\
**Post date:** [April 3, 2023, 11:27am UTC](https://discourse.julialang.org/t/creating-svector-of-a-single-svector-1-float64/96979/3 "2023-04-03T11:27:15Z")

</div>

Thank you @longemen3000, `SA` constructor does create nested SVectors even when both have `Size` 1 (i.e. `N=1` and `Dim=1`). But I would still like to understand what prevents the constructor with explicit type parameters (I have also tried directly using `SArray` constructor, without using the `SVector` alias, and got the same error). I checked the source code of [StaticArraysCore.jl](https://github.com/JuliaArrays/StaticArraysCore.jl/blob/main/src/StaticArraysCore.jl) but couldn’t understand why:  
A) `SVector` of a `Size`-2 `Svector` (or `Size`-2 `SVector` of `Size`-1 `SVector`s) either (1) uses the first inner construct of `SArray`, or (2) passes the `convert_tuple`,  
B) while a `SVector` of a `Size`-1 `Svector` fails in the `convert_tuple`.

Moreover, `SA` constructor seems to be much slower when passed an existing `SVector` and makes an extra allocation, compared to passing directly the type parameters of the inner `SVector`. [See a similar discussion on creating SVector of SVectors](https://discourse.julialang.org/t/how-to-create-an-svector-of-svectors-part-ii/61109)

```julia
julia> my_vector_2d
2-element SVector{2, Float64} with indices SOneTo(2):
 0.8
 0.9

julia> @benchmark SA[my_vector_2d]
BenchmarkTools.Trial: 10000 samples with 590 evaluations.
 Range (min … max): 197.217 ns … 6.917 μs ┊ GC (min … max): 0.00% … 96.72%
 Time (median): 209.234 ns ┊ GC (median): 0.00%
 Time (mean ± σ): 230.900 ns ± 153.116 ns ┊ GC (mean ± σ): 1.39% ± 2.16%

  ▅▇█▇▃ ▂▂▁ ▁▁▂ ▁
  █████▇████▇██████████▇▇▆█▇███▇▇▇▆▆▆▆▆▆▆▆▇▆▆▆▆▅▆▆▅▆▅▅▆▅▅▅▆▅▅▅▅ █
  197 ns Histogram: log(frequency) by time 486 ns <

 Memory estimate: 64 bytes, allocs estimate: 2.

julia> @benchmark SVector{1, SVector{2, Float64}}(my_vector_2d)
BenchmarkTools.Trial: 10000 samples with 942 evaluations.
 Range (min … max): 79.872 ns … 4.579 μs ┊ GC (min … max): 0.00% … 98.13%
 Time (median): 82.801 ns ┊ GC (median): 0.00%
 Time (mean ± σ): 93.011 ns ± 85.076 ns ┊ GC (mean ± σ): 1.75% ± 1.95%

  ▇█▇▂ ▁▂▁▂▃ ▁▁ ▁ ▁
  ████▇▇▇▆█████▆▅▆▇████▇████▇▇▇██▆▆▆▅▆▆▇▇▇▆▆▅▅▅▅▆▅▆▆▅▆▅▅▄▄▄▅▅ █
  79.9 ns Histogram: log(frequency) by time 201 ns <

 Memory estimate: 32 bytes, allocs estimate: 1.

```

and here is an MWE without benchmarks:

```julia
using BenchmarkTools, StaticArrays

# Inner SVectors
my_vector_1d = SVector{1, Float64}(0.8)
my_vector_2d = SVector{2, Float64}(0.8, 0.9)

# Container SVectors
# Size-1 SVector of Size-1 SVector
# my_container_faulty = SVector{1, SVector{1, Float64}}(my_vector_1d) # gives error
my_container_a = SA[my_vector_1d]
# Size-2 SVector of Size-1 SVectors
my_container_b = SVector{2, SVector{1, Float64}}(my_vector_1d, my_other_vector_1d)
# Size-1 SVector of Size-2 Svector
my_container_c = SVector{1, SVector{2, Float64}}(my_vector_2d)
```

---

_[View the full topic](https://discourse.julialang.org/t/creating-svector-of-a-single-svector-1-float64/96979)._