# Best practices for organizing objects

**URL:** <https://discourse.julialang.org/t/best-practices-for-organizing-objects/108305>\
**Category:** General Usage\
**Tags:** question, mutable-structure\
**Created:** [January 3, 2024, 2:49pm UTC](https://discourse.julialang.org/t/best-practices-for-organizing-objects/108305 "2024-01-03T14:49:08Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Gast](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gast/32/206425_2.png) [@Gast](https://discourse.julialang.org/u/Gast)\
**Post date:** [January 3, 2024, 2:49pm UTC](https://discourse.julialang.org/t/best-practices-for-organizing-objects/108305/1 "2024-01-03T14:49:08Z")

</div>

I wonder if how I call objects through different functions is the ‘best way’ of doing it (or if at least is in line with Julia’s best practices). A general example of what I am doing is below.

All objects needed in my program (e.g., variables or parameters) are collected in a specific `module` with different `mutable` structures. This module is saved in a separate `.jl` file:

```julia
module Globals

    export a, b, c

    mutable struct A
        ....
    end

    a = A()

    mutable struct B
        ....
    end

    b = B()

    mutable struct C
        ....
    end

    c = C()

end

```

In the `main.jl` file of my program, I import the module `Globals` and also call different functions that use the objects inside the module:

```julia
@everywhere include("globals.jl")                   
using .Globals
import .Globals: a, b, c

a.do_something = true        
foo(a, b)

c.something = foo2(b)

foo3(a, c)

```

Some objects defined in `struct` `A`, `B`, and `C` are empty until a particular function is called and defined in a very general way (e.g., `x1::Any = Nothing()`).

I am wondering if this way of structuring my program is, e.g., more efficient than other ways, like pre-defining my objects within each function instead of importing them from the module `Globals`? In general, the sketch above would be in line with Julia’s best practices? Any advice/thoughts on this is very welcome!

Thanks!

---

<div class="post-metadata">

**Author:** ![stevengj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevengj/32/71_2.png) [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Post date:** [January 3, 2024, 2:58pm UTC](https://discourse.julialang.org/t/best-practices-for-organizing-objects/108305/2 "2024-01-03T14:58:28Z")

</div>

> [@Gast](#):
>
> `module Globals`

It’s generally better (for style, performance, maintainability) to avoid global variables entirely if you can. [Global variables tend to be slow](https://docs.julialang.org/en/v1/manual/performance-tips/#Avoid-untyped-global-variables) in Julia, but the overall idea that usage of global variables should be kept to a minimum is common throughout software engineering — google “avoid global variables” to find lots of commentary on this.

---

<div class="post-metadata">

**Author:** ![Gast](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gast/32/206425_2.png) [@Gast](https://discourse.julialang.org/u/Gast)\
**Post date:** [January 3, 2024, 4:06pm UTC](https://discourse.julialang.org/t/best-practices-for-organizing-objects/108305/3 "2024-01-03T16:06:46Z")

</div>

Would using function arguments to pass objects between functions be a way to avoid global variables?

In other words, instead of generating an instance of my `A` structure in the `module Globals`, I could allow each of my functions to create an instance of the `A` structure and thus manipulate a shared object (say, `x1`) within each function:

```julia
struct A
    x1::Any
end

```

```julia
function foo()
    a = A(0)
    
    foo2() = begin
        a.x1 += 1
    end
    
    foo3() = begin
        a.x1 = 0
    end
    
    return foo2, foo3
end

increment, reset = foo()

```

---

<div class="post-metadata">

**Author:** ![stevengj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stevengj/32/71_2.png) [@stevengj](https://discourse.julialang.org/u/stevengj)\
**Post date:** [January 3, 2024, 4:45pm UTC](https://discourse.julialang.org/t/best-practices-for-organizing-objects/108305/4 "2024-01-03T16:45:47Z")

</div>

> [@Gast](#):
>
> Would using function arguments to pass objects between functions be a way to avoid global variables?

Yes.

(Though your posted code is not an example of this — your functions don’t have any arguments!)