# An issue with dispatching imported types

**URL:** <https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004>\
**Category:** General Usage\
**Tags:** question\
**Created:** [October 30, 2024, 4:39pm UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004 "2024-10-30T16:39:01Z")\
**Posts on this page:** 20\
**Page:** 2

<div class="post-metadata">

**Author:** ![lmiq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/lmiq/32/18314_2.png) [@lmiq](https://discourse.julialang.org/u/lmiq)\
**Post date:** [October 31, 2024, 8:12pm UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/21 "2024-10-31T20:12:28Z")

</div>

Note that (AFAIK) `Revise` cannot delete a struct definition, just its methods. Thus, if I have a module:

```julia
module MyPkg
    struct A end
end

```

and thus, a struct that is defined inside the package:

```julia-repl
julia> includet("./MyPkg.jl")

julia> using .MyPkg

julia> MyPkg.A
Main.MyPkg.A

```

it does not disappear if the definition is deleted:

```julia
module MyPkg
end

```

```julia-repl
# after changing the file
julia> MyPkg.A
Main.MyPkg.A

```

which means that you need to restart you Julia section if you deleted those definitions inside `PeriodicSystems`.

ps: To use a clean new environment, start Julia and do:

```julia-repl
julia> ] activate --temp

julia> dev PeriodicSystems, PeriodicMatrices

julia> # ... do your tests

```

---

<div class="post-metadata">

**Author:** ![andreasvarga](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andreasvarga/32/11634_2.png) [@andreasvarga](https://discourse.julialang.org/u/andreasvarga)\
**Post date:** [October 31, 2024, 8:45pm UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/22 "2024-10-31T20:45:54Z")

</div>

I performed the steps as you indicated and then the test. The following error message is possibly relevant

```julia
julia> A = PeriodicSymbolicMatrix([cos(t) 1; 1 1-sin(t)],2*pi);
WARNING: both PeriodicMatrices and PeriodicSystems export "PeriodicSymbolicMatrix"; uses of it in module Main must be qualified
ERROR: UndefVarError: `PeriodicSymbolicMatrix` not defined
Stacktrace:
 [1] top-level scope
   @ REPL[9]:1

```

The loaded version of `PeriodicSystems` corresponds to the current version v0.8.0, which contains the old definitions.

```julia
(jl_35CxA4) pkg> st
Status `C:\Users\Andreas\AppData\Local\Temp\jl_35CxA4\Project.toml`
  [dd9cd634] PeriodicMatrices v0.1.1 `C:\Users\Andreas\.julia\dev\PeriodicMatrices`
  [5decd0d0] PeriodicSystems v0.8.0 `C:\Users\Andreas\.julia\dev\PeriodicSystems`

```

This explains the above error message.

---

<div class="post-metadata">

**Author:** ![kellertuer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kellertuer/32/220707_2.png) [@kellertuer](https://discourse.julialang.org/u/kellertuer)\
**Post date:** [October 31, 2024, 9:02pm UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/23 "2024-10-31T21:02:05Z")

</div>

yeah, the `dev` command you did, took the two packages in development mode, but from the `.Julia/` folder, not from your local hard drive. That is why those are the old ones.

---

<div class="post-metadata">

**Author:** ![andreasvarga](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andreasvarga/32/11634_2.png) [@andreasvarga](https://discourse.julialang.org/u/andreasvarga)\
**Post date:** [November 1, 2024, 10:19am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/24 "2024-11-01T10:19:14Z")

</div>

> [@lmiq](#):
>
> it does not disappear if the definition is deleted:

This could be the issue: the old structures are somehow still present, and this leads to ambiguities. Is any way to get rid of the existing precompilations? I ponder to start from scratch to rebuild PeriodicSystems, with another name, as a new package. This should work without problems, or ?.

---

<div class="post-metadata">

**Author:** ![lmiq](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/lmiq/32/18314_2.png) [@lmiq](https://discourse.julialang.org/u/lmiq)\
**Post date:** [November 1, 2024, 10:25am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/25 "2024-11-01T10:25:01Z")

</div>

In principle restarting Julia should be enough.

---

<div class="post-metadata">

**Author:** ![kellertuer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kellertuer/32/220707_2.png) [@kellertuer](https://discourse.julialang.org/u/kellertuer)\
**Post date:** [November 1, 2024, 10:42am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/26 "2024-11-01T10:42:43Z")

</div>

A breaking release should be fine, since you remove Features (like the struct we discuss). No need for a new name.

---

<div class="post-metadata">

**Author:** ![andreasvarga](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andreasvarga/32/11634_2.png) [@andreasvarga](https://discourse.julialang.org/u/andreasvarga)\
**Post date:** [November 2, 2024, 9:54am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/27 "2024-11-02T09:54:41Z")

</div>

I moved to a new breaking release (for the MWE) v0.9.0

```julia
(@v1.10) pkg> st PeriodicSystems
Status `C:\Users\Andreas\.julia\environments\v1.10\Project.toml`
  [5decd0d0] PeriodicSystems v0.9.0 `C:\Users\Andreas\Documents\software\Julia\PeriodicSystems.jl`

```

The sequence still fails:

```julia
julia> using PeriodicSystems

julia> using PeriodicMatrices

julia> A = PeriodicSymbolicMatrix(rand(2,2),2*pi);

julia> ps1(A)
ERROR: MethodError: no method matching ps1(::PeriodicSymbolicMatrix{:c, Num, Matrix{Num}})

Closest candidates are:
  ps1(::T) where T<:PeriodicMatrices.PeriodicSymbolicMatrix
   @ PeriodicSystems C:\Users\Andreas\Documents\software\Julia\PeriodicSystems.jl\src\PeriodicSystems.jl:6

Stacktrace:
 [1] top-level scope
   @ REPL[28]:1

```

However, the following works:

```julia
julia> A = PeriodicSystems.PeriodicSymbolicMatrix(rand(2,2),2*pi);

julia> ps1(A)
PeriodicMatrices.PeriodicSymbolicMatrix{:c, Num, Matrix{Num}}

```

Is this a step forward?

See also

```julia
julia> @which PeriodicSymbolicMatrix(rand(2,2),2*pi)
PeriodicSymbolicMatrix(F::VecOrMat{T}, period::Real; nperiod) where T<:Real
     @ PeriodicMatrices C:\Users\Andreas\Documents\software\Julia\PeriodicMatrices.jl\src\types\PeriodicMatrix_sym.jl:27

julia> @which PeriodicSystems.PeriodicSymbolicMatrix(rand(2,2),2*pi)
PeriodicMatrices.PeriodicSymbolicMatrix(F::VecOrMat{T}, period::Real; nperiod) where T<:Real
     @ PeriodicMatrices C:\Users\Andreas\.julia\packages\PeriodicMatrices\ZwH3j\src\types\PeriodicMatrix_sym.jl:27

```

Apparently the same function is called in both cases.

---

<div class="post-metadata">

**Author:** ![kellertuer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kellertuer/32/220707_2.png) [@kellertuer](https://discourse.julialang.org/u/kellertuer)\
**Post date:** [November 2, 2024, 10:27am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/28 "2024-11-02T10:27:17Z")

</div>

Oh, maybe I was not precise enough. Just changing the version number does not change the functionality, it is an indicator for users that there was a breaking change, so that they have to adapt their code.

You would still have to decide to move the definition of the `PeriodicSymbolicMatrix` to _exacty one_ package, otherwise you always have two such types.

Again, I can not see your dev version, so I can just guess:

You currently seem to define the type in _both_ packages still. This still creates two completely different types. It looks like, currently only one of them, `PeriodicMatrices` exports the type and hence only one is available in global scope.  
I conclude that from the fact that you can define `A` (and that `ps1` fails).

The `PeriodicSystems` tape is not exported, because that would cause an ambiguity and you would have to specify _which_ of the two types `A` should be of.

But then of course `ps1` is defined for the (non-exported, internal) data type of a `PeriodicSymbolicMatrix` within the `PeriodicSystems` which due to the two _completely different_ types is **not** the type of `A`. so sure the `ps1` call fails, unless you specifically use that type for which `ps1` is defined.

A good analogy is really again two people, maybe even born on the same day of same name.  
One lives in `PeriodicSystems`, one lives in `PeriodicMatrices` and that name is also exported (make known to) `Main` if you are `using` the package.  
They are still two completely different types (people) that just share the same name.

I see really only one solution here. Do not define the type twice. It now confuses you as the developer so it will confuse most of your users.  
I would do the following – also since you are “_extracting_” the matrices into their own package.

1. Define the type _only_ in `PeriodicMatrices` and export it there
2. Make `PeriodicMatrices` a dependency of `PeriodicSystems` and use the type that `PeriodicMatrices` defines therein as well

This can even be done in a non.breaking way, since someone only using `PeriodicSystems` would not even notice a difference.

Your last type of code confuses me though, because it seems you might have even done this already? Again, all of this post is merely written on _guessing_ what your current code status is. It would maybe be easier to actually do a small zoom meeting instead of this now really really long thread where we try to reverse-engineer from your errors both what you current package status and REPL status is.

The main message and thing to follow is: Do not define the type twice. Define it once and only use it in the other package then (that of course then depends on the one where you define it).

---

<div class="post-metadata">

**Author:** ![andreasvarga](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andreasvarga/32/11634_2.png) [@andreasvarga](https://discourse.julialang.org/u/andreasvarga)\
**Post date:** [November 2, 2024, 10:36am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/29 "2024-11-02T10:36:35Z")

</div>

> [@kellertuer](#):
>
> Your last type of code confuses me though, because it seems you might have even done this already?

Yes, I did.

---

<div class="post-metadata">

**Author:** ![kellertuer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kellertuer/32/220707_2.png) [@kellertuer](https://discourse.julialang.org/u/kellertuer)\
**Post date:** [November 2, 2024, 10:38am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/30 "2024-11-02T10:38:16Z")

</div>

Then your first code is still running on a version of REPL / running Julia where that change had not yet taken effect (i.e. you still need to restart REPL).

---

<div class="post-metadata">

**Author:** ![andreasvarga](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andreasvarga/32/11634_2.png) [@andreasvarga](https://discourse.julialang.org/u/andreasvarga)\
**Post date:** [November 2, 2024, 10:40am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/31 "2024-11-02T10:40:08Z")

</div>

> [@kellertuer](#):
>
> The main message and thing to follow is: Do not define the type twice. Define it once and only use it in the other package then (that of course then depends on the one where you define it).

The type is defined only once in `PeriodicMatrices`. No type definitions take place in `PeriodicSystems`.

---

<div class="post-metadata">

**Author:** ![kellertuer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kellertuer/32/220707_2.png) [@kellertuer](https://discourse.julialang.org/u/kellertuer)\
**Post date:** [November 2, 2024, 10:43am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/32 "2024-11-02T10:43:36Z")

</div>

> [@andreasvarga](#):
>
> The type is defined only once in `PeriodicMatrices`. No type definitions take place in `PeriodicSystems`.

That contradicts what you wrote earlier that

> [@andreasvarga](#):
>
> ```julia
> julia> A = PeriodicSymbolicMatrix(rand(2,2),2*pi);
> 
> julia> ps1(A)
> ERROR: MethodError: no method matching ps1(::PeriodicSymbolicMatrix{:c, Num, Matrix{Num}})
> 
> Closest candidates are:
> ps1(::T) where T<:PeriodicMatrices.PeriodicSymbolicMatrix
> @ PeriodicSystems C:\Users\Andreas\Documents\software\Julia\PeriodicSystems.jl\src\PeriodicSystems.jl:6
> 
> ```

unless that was in a REPL session where the old definition was still present, but again, this is by now merely guesswork and a bit hard to reverse-engineer without knowing the code base and REPL state you run code in.

---

<div class="post-metadata">

**Author:** ![andreasvarga](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andreasvarga/32/11634_2.png) [@andreasvarga](https://discourse.julialang.org/u/andreasvarga)\
**Post date:** [November 2, 2024, 10:44am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/33 "2024-11-02T10:44:40Z")

</div>

> [@kellertuer](#):
>
> you still need to restart REPL

I am not sure I understood this. I am working in VSCode, so any time I restart Julia, I restart also REPL. Or ?

---

<div class="post-metadata">

**Author:** ![kellertuer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kellertuer/32/220707_2.png) [@kellertuer](https://discourse.julialang.org/u/kellertuer)\
**Post date:** [November 2, 2024, 10:47am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/34 "2024-11-02T10:47:01Z")

</div>

Ah yes with restarting REPL I mean to do `julia>quit()` or control+d and then start Julia again _or_ start a new Terminal in VS code.

The simple reason is, that there is no way to “unload” or “`unusing`” a package. For functions `Revise.jl` is super helpful but whenever you change structs (or also move them to new packages) you have to restart julia.

---

<div class="post-metadata">

**Author:** ![andreasvarga](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andreasvarga/32/11634_2.png) [@andreasvarga](https://discourse.julialang.org/u/andreasvarga)\
**Post date:** [November 2, 2024, 10:58am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/35 "2024-11-02T10:58:47Z")

</div>

The whole `PeriodicSystems` package consists of the following:

```julia
module PeriodicSystems

using PeriodicMatrices

function ps1(A::T) where {T <: PeriodicSymbolicMatrix}
    return typeof(A)
end

export ps1

end

```

As you can see, there are now new type definitions, and `ps1` is the only function in this package (excepting those imported from `PeriodicMatrices`).  
I wonder if using `Reexport` could be helpful.

---

<div class="post-metadata">

**Author:** ![kellertuer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kellertuer/32/220707_2.png) [@kellertuer](https://discourse.julialang.org/u/kellertuer)\
**Post date:** [November 2, 2024, 11:14am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/36 "2024-11-02T11:14:41Z")

</div>

Well. Again. I can not reproduce the error you report above with the code you post here.

For reproducibility: I start Julia, I activate a temporary environment, I install `PeriodicMatrices` (I fetch a coffee while it complies 😉 ) and then do the following

```repl
(jl_vBrjwG) pkg> status
Status `/private/var/folders/_v/wg192lpd3mb1lp55zz7drpcw0000gn/T/jl_vBrjwG/Project.toml`
  [dd9cd634] PeriodicMatrices v0.1.1

julia> module PeriodicSystems

       using PeriodicMatrices

       function ps1(A::T) where {T <: PeriodicSymbolicMatrix}
           return typeof(A)
       end

       export ps1

       end
Main.PeriodicSystems

julia> using .PeriodicSystems

julia> A = PeriodicSymbolicMatrix(rand(2,2),2*pi);
ERROR: UndefVarError: `PeriodicSymbolicMatrix` not defined in `Main`
Suggestion: check for spelling errors or missing imports.
Hint: a global variable of this name may be made accessible by importing PeriodicMatrices in the current active module Main
Stacktrace:
 [1] top-level scope
   @ REPL[6]:1

julia> using PeriodicMatrices

julia> A = PeriodicSymbolicMatrix(rand(2,2),2*pi);

julia> ps1(A)
PeriodicSymbolicMatrix{:c, Symbolics.Num, Matrix{Symbolics.Num}}

```

So all works as I wrote above. We just have one definition of `PeriodicSymbolicMatrix`, namely in `PeriodicMatrices`.  
You are right, since `PeriodicSystems` does not export it, we are explicitly required to load `PeriodicMatrices` to be able to construct `A`, otherwise (see first try) that name does simply not exist in `Main`.

But as soon as I do load `PeriodicMatrices` I _can_ define `A` but then of course also `ps1` just works fine because in this scenario we just have one such type and within `PeriodicSystems` and in `Main` both names refer to exactly the same type.

So I am not sure how you got to an error above, unless your Julia session was not freshly started and there were some old remedies of existing types _or_ you used `using PeriodicSystems` and have that installed or in dev mode in that environment as well – then it dies not load the module you define on REPL, as you can see my code has to use `using .PeriodicSystems` to load the module I define on REPL.

---

<div class="post-metadata">

**Author:** ![andreasvarga](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andreasvarga/32/11634_2.png) [@andreasvarga](https://discourse.julialang.org/u/andreasvarga)\
**Post date:** [November 2, 2024, 11:33am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/37 "2024-11-02T11:33:45Z")

</div>

Updating Julia, say to v1.11, could help ?

---

<div class="post-metadata">

**Author:** ![kellertuer](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kellertuer/32/220707_2.png) [@kellertuer](https://discourse.julialang.org/u/kellertuer)\
**Post date:** [November 2, 2024, 11:46am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/38 "2024-11-02T11:46:24Z")

</div>

I think that does not make a difference. While I could not install the most recent version on 1.8 or 1.9 (maybe it needs at least 1.10?) on 1.10 the last example I posted runs 100% the same results.

---

<div class="post-metadata">

**Author:** ![andreasvarga](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andreasvarga/32/11634_2.png) [@andreasvarga](https://discourse.julialang.org/u/andreasvarga)\
**Post date:** [November 2, 2024, 12:26pm UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/39 "2024-11-02T12:26:31Z")

</div>

I changed the module definition to

```julia
module PeriodicSystems

using Reexport
@reexport using PeriodicMatrices

function ps1(A::T) where {T <: PeriodicSymbolicMatrix}
    return typeof(A)
end

export ps1

end

```

Now it works:

```julia
julia> A = PeriodicSystems.PeriodicSymbolicMatrix(rand(2,2),2*pi);

julia> ps1(A)
PeriodicMatrices.PeriodicSymbolicMatrix{:c, Symbolics.Num, Matrix{Symbolics.Num}}

```

I will continue now with some more serious tests.

---

<div class="post-metadata">

**Author:** ![andreasvarga](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/andreasvarga/32/11634_2.png) [@andreasvarga](https://discourse.julialang.org/u/andreasvarga)\
**Post date:** [November 9, 2024, 11:37am UTC](https://discourse.julialang.org/t/an-issue-with-dispatching-imported-types/122004/40 "2024-11-09T11:37:03Z")

</div>

@lmiq and @kellertuer: I would like to thank for your time and patience assisting me to overcome this issue. I would still like to stress that, although the above solution works, I don’t have the full understanding what is different from the original implementation. Furthermore, I wonder if some side effects still can occur. In any case, I will register a new breaking release of `PeriodicSystems`, before other developments take place.

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