朱莉娅:将元素追加到自定义类型的数组中 [英] Julia: Append an element to an array of custom types

问题描述

在Julia中将元素添加到数组的工作原理如下:

Appending an element to an array in Julia works like this:

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

当我尝试使用自定义类型

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))

我收到以下错误:

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

我假设我必须实现" length方法，但是不知道如何.

I assume I have to 'implement' the length method but do not know how.

推荐答案

append!命令不会执行您认为的操作.您正在考虑push!命令.

The append! command doesn't do what you think it does. You're thinking of the push! command.

append!命令将附加到两个数组中.这两个参数都必须是数组:

The append! command appends two arrays together. Both arguments need to be arrays:

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

否length实施必要的
_{(该错误只是告诉您它试图读取第二个参数的数组长度，发现不是数组的东西.)}

No length implementing necessary
_{(that error was just telling you it tried to read the length of your array for the second argument and found something that was not an array.)}

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