CODEWITHSUNDEEP
julia
Jeting Wu
Jeting Wu

Reputation: 21

Troubles on user defined type in array using julia

I have some troubles using array containing user-defined type. A simple code goes like this:

struct MyType
 a::Int64
 b::Int64
end

MyArray = Array{MyType}(5)
MyArray[1].a = [1 2 3]

The compiler shows an error message "UnderRefError: access to undefined reference" Is this the problem due to there is no default constructor for MyType?

Upvotes: 1

Views: 207

Answers (2)

Gnimuc
Gnimuc

Reputation: 8566

In fact, there is always a default inner constructor automatically defined by Julia if you don't explicitly define one. It's equivalent to :

julia> struct MyType
         a::Int64
         b::Int64
         MyType(a,b) = new(a,b)
       end

Note that, by running MyArray = Array{MyType}(5), you just construct an 5-element array whose eltype should be MyType. Julia still doesn't know what on earth those entries are, that's what the error is complaining about. Take a look at the following example:

julia> a = Array{Complex}(5)
5-element Array{Complex{T<:Real},1}:
 #undef
 #undef
 #undef
 #undef
 #undef

btw, I don't know what you mean to do with this line MyArray[1].a = [1 2 3], since a is of type Int, not Vector{Int}.

Upvotes: 4

Erik Engheim
Erik Engheim

Reputation: 8512

This line doesn't make sense

MyArray[1].a = [1 2 3]

You got to write something like

MyArray[1] = MyType(4, 5)

because the first element of the MyArray array isn't defined. MyArray[1].a means you are trying to access the a member of an undefined object. That isn't going to work.

If you want to create an initialized 5 element array of MyType objects you can do something like this instead.

fill(MyType(0, 0), 10)

Upvotes: 3

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