# Referencing the same module from multiple files
**URL:** https://discourse.julialang.org/t/referencing-the-same-module-from-multiple-files/77775
**Category:** New to Julia
**Tags:** question, module, modules
**Created:** [March 12, 2022, 2:44am UTC](https://discourse.julialang.org/t/referencing-the-same-module-from-multiple-files/77775 "2022-03-12T02:44:48Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@knttnk](https://discourse.julialang.org/u/knttnk)
#### Post date: [March 12, 2022, 2:44am UTC](https://discourse.julialang.org/t/referencing-the-same-module-from-multiple-files/77775/1 "2022-03-12T02:44:48Z")
# Reproducible code
I created 3 files like
```julia-auto
# useful.jl
module Useful # issue
struct UsefulStruct
data
end
end
```
```julia-auto
# create.jl
module Create
include("useful.jl")
function create()::Useful.UsefulStruct
Useful.UsefulStruct(1)
end
end
```
```julia-auto
# calculate.jl
module Calculate
include("useful.jl")
include("create.jl")
calculate(s::Useful.UsefulStruct) = s.data * 2
end
```
in a directory, ran
```julia-auto
include("create.jl")
include("calculate.jl")
Calculate.calculate(
Create.create()
)
```
and got following error.
```julia-auto
ERROR: LoadError: MethodError: no method matching calculate(::Main.Create.Useful.UsefulStruct)
Closest candidates are:
calculate(::Main.Calculate.Useful.UsefulStruct) at /...
```
# Question
I thought I was using the same `UsefulStruct`, but it is recognized as something different.
What should I do if I want to do these things?
---
### Author:  [@Henrique\_Becker](https://discourse.julialang.org/u/Henrique_Becker)
#### Post date: [March 12, 2022, 3:29am UTC](https://discourse.julialang.org/t/referencing-the-same-module-from-multiple-files/77775/2 "2022-03-12T03:29:05Z")
Welcome to our community! 🎊
This problem is frequent among novice Julia programmers and was already asked multiple times in this forum. (But I concede that the search utility of Discourse **never** finds any useful results, even when I know they exist.) See:
> [@MethodError: no method matching, but the method exists](https://discourse.julialang.org/t/methoderror-no-method-matching-but-the-method-exists/54767):
>
> I’m getting the following error: ERROR: MethodError: no method matching choose(::Main.Sim.ModelBasedAgent, ::Int64) Closest candidates are: choose(::Main.Sim.ModelFreeAgent, ::Int64) at /home/xxxxx/Projects/simulateagents.jl:57 choose(::Main.Sim.ModelBasedAgent, ::Int64) at /home/xxxxx/Projects/simulateagents.jl:53 But there is a matching method. What’s going on?
> [@Dependencies of src files inside a package](https://discourse.julialang.org/t/dependencies-of-src-files-inside-a-package/43144/3):
>
> Technically, I agree with @rdeits. However, I’m not sure that’s really the solution you are looking for. My experience I have experienced the same confusion myself, and I have noticed that others seem to be stuck in the same mindset. I think it might stem from our ingrained C/C++'s include/header file methodology (assuming that’s your background). In most cases, I don’t really want to break things up into different modules - especially inside a single package. Typically, when I need to bre…
Basically, the rule is: _include **once** and import whenever necessary_.
Your topmost module should **include** all files a single time and you should use `import`/`using` relative to it (`using .MyModule` refers to a module defined in the current module, `using ..MyModule` refers to a module define in the parent module, i.e., a sibling module, and you can do something like `using ...MyModule.A.B` to go to the parent of the parent and then go down to a specific submodule). In your case, if you `include` `Useful` and `Create` inside `Calculate` you want to replace the `include("useful.jl")` inside `Create` by `import ..Useful`
---
### Author:  [@knttnk](https://discourse.julialang.org/u/knttnk)
#### Post date: [March 13, 2022, 2:49am UTC](https://discourse.julialang.org/t/referencing-the-same-module-from-multiple-files/77775/3 "2022-03-13T02:49:43Z")
Thank you for your polite and kind reply!
It solved my problem.