Julia: add an element to an array of custom types

Question

Adding an element to an array in Julia works as follows:

v = Array{Int32, 1}(0) append!(v, 1) append!(v, 2) println(v) # prints: Int32[1,2] 

When I try this with a custom type

 type Node label::String value::Int32 end nodes = Array{Node, 1}(0) append!(nodes, Node("a", 42)) 

I get the following error:

 ERROR: LoadError: MethodError: no method matching length(::Node) 

I assume that I need to "implement" the length method, but I don’t know how to do it.

Answer 1

append! team Don't do what you think. Are you thinking of the push! team push! .

append! team combines two arrays. Both arguments must be arrays:

 julia> append!(nodes, [Node("a", 42)]) 1-element Array{Node,1}: Node("a",42) 

No length execution needed _{(this error just told you that it was trying to read the length of your array for the second argument and found that it was not an array.)}

Answer 2

try it

 Base.append!(x::Array{Node,1}, val::Node) = push!(x, val) 

then you get

 append!(nodes, Node("a", 42)) 1-element Array{Node,1}: Node("a",42) 

you need to explicitly create a function for this particular type, since append! or any of the Base functions sometimes (or maybe I always checked havent) don't accept Any