FixedSizeVectors with cache-aligned memory?

General Usage
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2

It has nothing to do with the implementation of AlignedAllocs, the FixedSizeArray type just doesn’t (yet) support directly wrapping an input DenseVector with a possibly different size. It’s just some uninitialized instantiation and collecting input AbstractArrays into new parent DenseVectors (currently defaulting to Memory), which is a bit strange because the latter seems to be what FixedSizeArrayDefault is intended for.

julia> methods(FixedSizeArray.body.body.body)
# 4 methods for type constructor:
 [1] (::Type{FSA})(::UndefInitializer, size::Tuple{Vararg{Integer}}) where {T, FSA<:(FixedSizeArray{T, N, Mem} where {N, Mem<:DenseVector{T}})}
     @ C:\Users\benm1\.julia\packages\FixedSizeArrays\22QFl\src\FixedSizeArray.jl:138
 [2] (::Type{FSA})(::UndefInitializer, size::Integer...) where {T, FSA<:(FixedSizeArray{T, N, Mem} where {N, Mem<:DenseVector{T}})}
     @ C:\Users\benm1\.julia\packages\FixedSizeArrays\22QFl\src\FixedSizeArray.jl:141
 [3] (::Type{FSA})(src::AbstractArray) where {N, FSA<:(FixedSizeArray{var"#s3", N, Mem} where {var"#s3", Mem<:DenseVector{var"#s3"}})}
     @ C:\Users\benm1\.julia\packages\FixedSizeArrays\22QFl\src\FixedSizeArray.jl:336
 [4] (::Type{FSA})(src::AbstractArray) where FSA<:FixedSizeArray
     @ C:\Users\benm1\.julia\packages\FixedSizeArrays\22QFl\src\FixedSizeArray.jl:343

We can verify with a minimal example type:

julia> begin
       # might be an incorrect subtype, but it'll serve the example
       mutable struct OneElement{T} <: DenseVector{T} value::T end
       Base.size(::OneElement) = (1,)
       Base.getindex(A::OneElement, i::Int) = if i == 1 A.value else throw(BoundsError(A, i)) end
       Base.setindex!(A::OneElement, v, i::Int) = if i == 1 A.value = v else throw(BoundsError(A, i)) end
       using FixedSizeArrays
       end

julia> FixedSizeArray(OneElement(2f0)) # input collected into parent Memory
1-element FixedSizeArray{Float32, 1, Memory{Float32}}:
 2.0

julia> FixedSizeVector(OneElement(2f0)) # of course aliases also do this
1-element FixedSizeArray{Float32, 1, Memory{Float32}}:
 2.0

There is only a private inner constructor(?) that can do this, but it’s not ideal because there isn’t an option to compute the size directly from the DenseVector and broadcasting fails at a with_stripped_type_parameters_unchecked call that is only implemented for Vector and GenericMemory.

julia> FixedSizeArrays.new_fixed_size_array(OneElement(2f0), (1,)) # no idea why the alias is printed
1-element FixedSizeVector{Float32, OneElement{Float32}}:
 2.0

julia> 1 .+ FixedSizeArrays.new_fixed_size_array(OneElement(2f0), (1,1))
ERROR: MethodError: no method matching with_stripped_type_parameters_unchecked(::FixedSizeArrays.TypeParametersElementType, ::Type{OneElement{Float32}})