CODEWITHSUNDEEP
julia
Hamlet
Hamlet

Reputation: 175

Structs of Arrays: Type Error

I do not get the difference between the following two struct definitions. The first works without any problems, while the second gives a Type Error:

julia> struct point1
           xy::Vector{Float64}
       end

julia> struct point2
           xy::Array{Float64,1}(2)
       end
ERROR: TypeError: point2: in type definition, expected Type, got Array{Float64,1}
Stacktrace:
 [1] eval(::Module, ::Any) at ./boot.jl:235
 [2] eval(::Any) at ./boot.jl:234
 [3] macro expansion at /Users/.julia/v0.6/Atom/src/repl.jl:186 [inlined]
 [4] anonymous at ./<missing>:?

Any ideas?

Upvotes: 1

Views: 272

Answers (2)

carstenbauer
carstenbauer

Reputation: 10157

The issue here is that Array{Float64,1}(2) isn't a type (i.e. typeof(Array{Float64,1}(2)) != DataType) but a newly initialized instance of a Array{Float64,1}.

If you would like to fix the dimension of the array field xy you can

1) make constructors throw errors/warnings if someone tries to initialize with an array of wrong size (this doesn't effect performance of course)

2) use StaticArrays.jl to maybe speed up your code

Pkg.add("StaticArrays")
using StaticArrays

struct point3
    xy::SVector{2,Float64}
end

Test:

julia> p = point3(@SVector rand(2))
point3([0.621778, 0.083348])

julia> p = point3(rand(2))
point3([0.737558, 0.405582])

julia> p = point3(rand(3))
ERROR: Dimension mismatch. Expected input array of length 2, got length 3

Upvotes: 4

Hamlet
Hamlet

Reputation: 175

Solved it:

struct point2
    xy::Array{Float64,1}
end

The problem was the definition of the dimension ...

Upvotes: 0

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