Something weird is going on with `DenseArray`

General Usage
, ,
1

From base/boot.jl:

# commented-out definitions are implemented in C

...

#abstract type AbstractArray{T,N} end
#abstract type DenseArray{T,N} <: AbstractArray{T,N} end

...

#mutable struct Array{T,N} <: DenseArray{T,N}
#  ref::MemoryRef{T}
#  size::NTuple{N,Int}
#end

So Array should be a subtype of DenseArray, and DenseArray should be abstract, so not a DataType. But these are apparently not true:

julia> Array{Int,3} isa DenseArray{Int,3}
false

julia> Array{Int,3} isa DenseArray
false

julia> Array isa DenseArray
false

julia> typeof(DenseArray{Int,3})
DataType

Although DenseArray and DenseArray{Int,3} have no constructor methods, as we would expect from an abstract type.

Is this a bug, or is there something I’m missing here?

2

isa and <: aren’t the same thing.

julia> Array{Int, 3} <: DenseArray{Int,3}
true
2 Likes
3

oh my god you’re right I’m just being dumb. and apparently DataTypes can be abstract too. I’m just gonna delete this.

4

FYI, the fact that abstract types usually don’t have (constructor) methods is purely a matter of style/convention. And some abstract types, like AbstractFloat, do have methods.