# Type alias interferes with construction
**URL:** https://discourse.julialang.org/t/type-alias-interferes-with-construction/121247
**Category:** General Usage
**Tags:** question, staticarrays
**Created:** [October 13, 2024, 1:07pm UTC](https://discourse.julialang.org/t/type-alias-interferes-with-construction/121247 "2024-10-13T13:07:12Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@prittjam](https://discourse.julialang.org/u/prittjam)
#### Post date: [October 13, 2024, 1:07pm UTC](https://discourse.julialang.org/t/type-alias-interferes-with-construction/121247/1 "2024-10-13T13:07:12Z")
Why does construction using the type alias for Hyperplane result in an error?
```julia
using FastClosures, GLMakie, Random, Distributions, Parameters, Rotations, StaticArrays, LinearAlgebra, CoordinateTransformations, Makie, Meshes, Unitful
const VectorNd{N} = SVector{N,Float64}
const Vector2d = VectorNd{2}
const Vector3d = VectorNd{3}
homogenize(x::Union{SVector, Meshes.Vec}) = push(x,one(eltype(x)))
struct Hyperplane{N} <: StaticVector{N, Float64}
v::VectorNd{N}
Hyperplane(v::VectorNd{N}) where N = new{N}(v / norm(v[1:N-1]))
end
@inline Base.getindex(p::Hyperplane, i::Int) = getindex(p.v, i)
@inline Tuple(p::Hyperplane) = Tuple(p.v)
const Line2 = Hyperplane{3}
Line2(SVector{3}(1.,2.,4.))
```
results in
> ERROR: DimensionMismatch: No precise constructor for Line2 found. Length of input was 3.
> Stacktrace:
> [1] \_no\_precise\_size(SA::Type, x::Tuple{Float64, Float64, Float64})
> @ StaticArrays ~/.julia/packages/StaticArrays/MSJcA/src/convert.jl:169
> [2] construct\_type(::Type{Line2}, x::StaticArrays.Args{Tuple{Tuple{Tuple{Float64, Float64, Float64}}}})
> @ StaticArrays ~/.julia/packages/StaticArrays/MSJcA/src/convert.jl:89
> [3] StaticArray (repeats 2 times)
> @ ~/.julia/packages/StaticArrays/MSJcA/src/convert.jl:173 [inlined]
> [4] Line2(sa::SVector{3, Float64})
> @ StaticArrays ~/.julia/packages/StaticArrays/MSJcA/src/convert.jl:180
> [5] top-level scope
> @ REPL[11]:1
Clearly I am missing something about the type system. Thank you.
---
### Author:  [@nsajko](https://discourse.julialang.org/u/nsajko)
#### Post date: [October 13, 2024, 1:57pm UTC](https://discourse.julialang.org/t/type-alias-interferes-with-construction/121247/2 "2024-10-13T13:57:16Z")
This isn’t related to the presence of `Line2`, or to the type system. You’ll get the same error by just writing `Hyperplane{3}` directly instead of `Line2`.
I’m not knowledgeable enough about the StaticArrays.jl interface that you’re implementing, but clearly either:
- you’re not implementing their interface correctly
- there’s a bug in StaticArrays.jl (less likely, I guess)
- you meant to add more constructors for your `struct`
---
### Author:  [@prittjam](https://discourse.julialang.org/u/prittjam)
#### Post date: [October 13, 2024, 3:13pm UTC](https://discourse.julialang.org/t/type-alias-interferes-with-construction/121247/3 "2024-10-13T15:13:35Z")
Yes, I see that. I don’t understand why the error occurs, though. I don’t think any constructors are missing.
---
### Author:  [@\_bernhard](https://discourse.julialang.org/u/_bernhard)
#### Post date: [October 13, 2024, 3:36pm UTC](https://discourse.julialang.org/t/type-alias-interferes-with-construction/121247/4 "2024-10-13T15:36:52Z")
Did not run the code, but i think that error occurs, because you don’t have a constructor for `Hyperplane` that explicitly takes the type parameter, but only one where the parameter is deduced from the argument, no?
So defining that (although it seems redundant at first) should fix the issue.
EDIT:
Basically, adding the following
```julia
Hyperplane{N}(v::VectorNd{N}) where N = Hyperplane(v)
```
---
### Author:  [@prittjam](https://discourse.julialang.org/u/prittjam)
#### Post date: [October 13, 2024, 3:47pm UTC](https://discourse.julialang.org/t/type-alias-interferes-with-construction/121247/5 "2024-10-13T15:47:08Z")
> [@\_bernhard](#):
>
> `Hyperplane{N}(v::VectorNd{N}) where N = Hyperplane(v)`
Yes, that works… thank you! It does seem redundant. I’ll have to think about why it is required.
---
### Author:  [@nsajko](https://discourse.julialang.org/u/nsajko)
#### Post date: [October 13, 2024, 3:59pm UTC](https://discourse.julialang.org/t/type-alias-interferes-with-construction/121247/6 "2024-10-13T15:59:30Z")
> [@prittjam](#):
>
> It does seem redundant. I’ll have to think about why it is required.
You define a constructor for `HyperPlane` above, not for `HyperPlane{3}`. The two clearly aren’t equal. Perhaps this section in the docs might be of use: [Constructors are just callable objects](https://docs.julialang.org/en/v1/manual/constructors/#Constructors-are-just-callable-objects)