# Creating struct to initialize array of arrays with function to push elements into that array

**URL:** <https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485>\
**Category:** General Usage\
**Tags:** question, data\_structures, function\
**Created:** [May 14, 2020, 6:22pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485 "2020-05-14T18:22:01Z")\
**Posts on this page:** 13\
**Page:** 1

<div class="post-metadata">

**Author:** ![wiktorkujawa](https://avatars.discourse-cdn.com/v4/letter/w/bc8723/32.png) [@wiktorkujawa](https://discourse.julialang.org/u/wiktorkujawa)\
**Post date:** [May 14, 2020, 6:22pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/1 "2020-05-14T18:22:02Z")

</div>

I want to create a function to push data into struct array. Here’s my code:

```julia
mutable struct graph{T}
  data::AbstractArray{Array{T,1},1}
  # addEdge(x,y)=push!(data[x],y) that doesn't work
end

# Creating method to assigns nodes
graph(nodes::T) where T = graph{T}([[] for i=1:nodes])
newGraph=graph(5)

```

I get that:

```julia
julia> newGraph=graph(5)
graph{Int64}(Array{Int64,1}[[], [], [], [], []])

```

and I can push elements like that:

```julia
push!(graph.data[1], 3)

```

but I want to do it in that way:

```julia
graph.addEdge(1,3)

```

and later input in the same way BFS or DFS algorithm functions, something like:

```julia
graph.BFS(2)

```

which will print the result of BFS (“2” is the root node in that case).  
Do you know the way to do this?

---

<div class="post-metadata">

**Author:** ![Oscar\_Smith](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oscar_smith/32/25343_2.png) [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)\
**Post date:** [May 14, 2020, 6:36pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/2 "2020-05-14T18:36:41Z")

</div>

So the problem is that you appear to have tried defining `addEdge` within `graph`, but in Julia the only times you define a function in a struct is for some types of constructors. Also, you probably want `graph` to be immutable, and rather than writing `AbstractArray{Array{T,1},1}`, you should probably just write `AbstractVector{Vector{T}}`.

```julia
struct graph{T}
    data::AbstractVector{Vector{T}}
end
graph(nodes::T) where T = graph{T}([[] for i=1:nodes])
addEdge!(G, x, y)=push!(G.data[x], y)
newGraph=graph(5)
addEdge!(newGraph, 1,3)

```

works as you want it to. The main lesson is that Julia isn’t Java (and that’s a good thing).

---

<div class="post-metadata">

**Author:** ![wiktorkujawa](https://avatars.discourse-cdn.com/v4/letter/w/bc8723/32.png) [@wiktorkujawa](https://discourse.julialang.org/u/wiktorkujawa)\
**Post date:** [May 14, 2020, 6:43pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/4 "2020-05-14T18:43:41Z")

</div>

No, that’s not the problem and that’s not the solution.

---

<div class="post-metadata">

**Author:** ![Oscar\_Smith](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oscar_smith/32/25343_2.png) [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)\
**Post date:** [May 14, 2020, 6:44pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/5 "2020-05-14T18:44:51Z")

</div>

What do you mean? After running that code, it gave the correct result.

---

<div class="post-metadata">

**Author:** ![wiktorkujawa](https://avatars.discourse-cdn.com/v4/letter/w/bc8723/32.png) [@wiktorkujawa](https://discourse.julialang.org/u/wiktorkujawa)\
**Post date:** [May 14, 2020, 6:45pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/6 "2020-05-14T18:45:37Z")

</div>

I don’t have problem with result. I want a way not a result.

---

<div class="post-metadata">

**Author:** ![Oscar\_Smith](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oscar_smith/32/25343_2.png) [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)\
**Post date:** [May 14, 2020, 6:47pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/7 "2020-05-14T18:47:31Z")

</div>

Julia is not an object oriented language and trying to make it into one will not be fun. You can get the syntax you want with a lot of work and closures, but it is very much recommended to write idiomatic Julia code rather than hacking together Java syntax in Julia.

---

<div class="post-metadata">

**Author:** ![wiktorkujawa](https://avatars.discourse-cdn.com/v4/letter/w/bc8723/32.png) [@wiktorkujawa](https://discourse.julialang.org/u/wiktorkujawa)\
**Post date:** [May 14, 2020, 7:02pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/8 "2020-05-14T19:02:30Z")

</div>

I know, If there were classes in Julia that would be easier to get this what I want.

---

<div class="post-metadata">

**Author:** ![wiktorkujawa](https://avatars.discourse-cdn.com/v4/letter/w/bc8723/32.png) [@wiktorkujawa](https://discourse.julialang.org/u/wiktorkujawa)\
**Post date:** [May 14, 2020, 7:49pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/9 "2020-05-14T19:49:13Z")

</div>

Maybe there’s a way. I wrote something like that and it seems to behave like I want:

```julia
struct Solution{T<:Number,S<:Function}
  data::Vector{T}
  printFunction::S
end

a=Solution(Int32[1; 2; 3], function NameDoesntMatter() print("Whatever") end)

```

```julia
julia> a.data
3-element Array{Int32,1}:
 1
 2
 3
julia> a.printFunction()
Whatever

```

I’ll try to expand this.

---

<div class="post-metadata">

**Author:** ![wiktorkujawa](https://avatars.discourse-cdn.com/v4/letter/w/bc8723/32.png) [@wiktorkujawa](https://discourse.julialang.org/u/wiktorkujawa)\
**Post date:** [May 14, 2020, 9:06pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/10 "2020-05-14T21:06:02Z")

</div>

Ok, I’ve found the answer:

```julia
struct graph{T<:Array{Array{Int64,1},1},S<:Function}
  data::T
  addEdge::S
end

root=graph([Int[] for i=1:5], function addEdge(x,y) push!(root.data[x],y) end)

```

Output:

```julia
julia> root=graph([Int[] for i=1:5], function addEdge(x,y) push!(root.data[x],y) end)
graph{Array{Array{Int64,1},1},typeof(addEdge)}(Array{Int64,1}[[], [], [], [], []], addEdge)

julia> root.data
5-element Array{Array{Int64,1},1}:
 []
 []
 []
 []
 []

julia> root.addEdge(1,5)
1-element Array{Int64,1}:
 5

julia> root.data
5-element Array{Array{Int64,1},1}:
 [5]
 []
 []
 []
 []

```

---

<div class="post-metadata">

**Author:** ![Oscar\_Smith](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oscar_smith/32/25343_2.png) [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)\
**Post date:** [May 14, 2020, 9:14pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/11 "2020-05-14T21:14:08Z")

</div>

This will break if you change the name of your graph. This is a really bad idea.

---

<div class="post-metadata">

**Author:** ![wiktorkujawa](https://avatars.discourse-cdn.com/v4/letter/w/bc8723/32.png) [@wiktorkujawa](https://discourse.julialang.org/u/wiktorkujawa)\
**Post date:** [May 14, 2020, 9:22pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/12 "2020-05-14T21:22:13Z")

</div>

1. This is just a try, I’m not sure if it is even functional.
2. Why would I want to change the name of declared graph  
3)“This will break if you change the name of your graph?”

```julia
struct initGraph{T<:Array{Array{Int64,1},1},S<:Function}
  data::T
  addEdge::S
end

nodes=5

graph=initGraph([Int[] for i=1:nodes], function addEdge(x,y) push!(graph.data[x],y) end)
graph2=initGraph([Int[] for i=1:nodes], function addEdge(x,y) push!(graph2.data[x],y) end)
graph3=initGraph([Int[] for i=1:nodes], function addEdge(x,y) push!(graph3.data[x],y) end)
graph4=initGraph([Int[] for i=1:nodes], function addEdge(x,y) push!(graph4.data[x],y) end)
graph5=initGraph([Int[] for i=1:nodes], function addEdge(x,y) push!(graph5.data[x],y) end)

```

---

<div class="post-metadata">

**Author:** ![Henrique\_Becker](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/henrique_becker/32/15443_2.png) [@Henrique\_Becker](https://discourse.julialang.org/u/Henrique_Becker)\
**Post date:** [May 14, 2020, 9:48pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/13 "2020-05-14T21:48:33Z")

</div>

I am not sure if I understand your problem, the question is “do you really really want to have this `graph.addEdge(1,3)` syntax?” Because what you are doing works, but it does create a new closure for each graph object, and forces you to have a abstract type field in your struct what is also not very good for performance. It is the syntax the problem? Because just doing:

```julia
add_edge!(g, i, v) = push!(g.data[i], v)
add_edge!(my_graph_obj, 1, 3)

```

would have better performance and would be a far more “Julian” way to do it.

---

<div class="post-metadata">

**Author:** ![wiktorkujawa](https://avatars.discourse-cdn.com/v4/letter/w/bc8723/32.png) [@wiktorkujawa](https://discourse.julialang.org/u/wiktorkujawa)\
**Post date:** [May 14, 2020, 10:07pm UTC](https://discourse.julialang.org/t/creating-struct-to-initialize-array-of-arrays-with-function-to-push-elements-into-that-array/39485/14 "2020-05-14T22:07:35Z")

</div>

That’s more about what I can do with Julia types. More of experimenting. Also as I don’t create any methods for the graph there is no need to create struct in this case.  
Just:

```julia
nodes=5
graph=[Int[] for i=1:nodes]
add_edge!(g, i, v) = push!(g[i], v)
add_edge!(graph, 1, 3)

```