# Why doesn't work the module 'const Ref{Task}(@async nothing)' in my package?

**URL:** <https://discourse.julialang.org/t/why-doesnt-work-the-module-const-ref-task-async-nothing-in-my-package/62132>\
**Category:** General Usage\
**Tags:** question\
**Created:** [May 31, 2021, 1:07pm UTC](https://discourse.julialang.org/t/why-doesnt-work-the-module-const-ref-task-async-nothing-in-my-package/62132 "2021-05-31T13:07:58Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Impressium](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/impressium/32/19575_2.png) [@Impressium](https://discourse.julialang.org/u/Impressium)\
**Post date:** [May 31, 2021, 1:07pm UTC](https://discourse.julialang.org/t/why-doesnt-work-the-module-const-ref-task-async-nothing-in-my-package/62132/1 "2021-05-31T13:07:58Z")

</div>

Hey all,

why can’t I use a module const like

```julia
module A
const TEST = Ref{Task}(@async nothing)
end

```

in a package.

```julia
(@v1.6) pkg> update
    Updating git-repo `C:\ProjectName\packages\julia\ProjectName`
    Updating `C:\Users\UserName\.julia\environments\v1.6\Project.toml`
  [e4102d56] ~ ProjectName v0.2.1 `C:\ProjectName\packages\julia\ProjectName#master` ⇒ v0.2.1 `C:\ProjectName\packages\julia\ProjectName#master`
    Updating `C:\Users\UserName\.julia\environments\v1.6\Manifest.toml`
  [e4102d56] ~ ProjectName v0.2.1 `C:\ProjectName\packages\julia\ProjectName#master` ⇒ v0.2.1 `C:\ProjectName\packages\julia\ProjectName#master`
Precompiling project...
  ✗ ProjectName
  0 dependencies successfully precompiled in 2 seconds (43 already precompiled)       
  1 dependency errored. To see a full report either run `import Pkg; Pkg.precompile()` or load the package

julia> using ProjectName
[Info: Precompiling ProjectName [e4102d56-39a5-47ec-876b-10baf1c2b503]
fatal: error thrown and no exception handler available.
ErrorException("Task cannot be serialized")
jl_error at /cygdrive/c/buildbot/worker/package_win64/build/src\rtutils.c:41
jl_serialize_value_ at /cygdrive/c/buildbot/worker/package_win64/build/src\dump.c:678 
jl_serialize_value_ at /cygdrive/c/buildbot/worker/package_win64/build/src\dump.c:787 
[inlined]
jl_serialize_value_ at /cygdrive/c/buildbot/worker/package_win64/build/src\dump.c:798 
jl_serialize_value_ at /cygdrive/c/buildbot/worker/package_win64/build/src\dump.c:330 
[inlined]
jl_serialize_module at /cygdrive/c/buildbot/worker/package_win64/build/src\dump.c:361 
jl_serialize_value_ at /cygdrive/c/buildbot/worker/package_win64/build/src\dump.c:675 
jl_serialize_value_ at /cygdrive/c/buildbot/worker/package_win64/build/src\dump.c:387 
[inlined]
jl_serialize_value_ at /cygdrive/c/buildbot/worker/package_win64/build/src\dump.c:507 
jl_serialize_value_ at /cygdrive/c/buildbot/worker/package_win64/build/src\dump.c:387 
[inlined]
jl_save_incremental at /cygdrive/c/buildbot/worker/package_win64/build/src\dump.c:2183jl_write_compiler_output at /cygdrive/c/buildbot/worker/package_win64/build/src\precompile.c:65
jl_atexit_hook at /cygdrive/c/buildbot/worker/package_win64/build/src\init.c:211      
repl_entrypoint at /cygdrive/c/buildbot/worker/package_win64/build/src\jlapi.c:703    
mainCRTStartup at /cygdrive/c/buildbot/worker/package_win64/build/cli\loader_exe.c:51 
BaseThreadInitThunk at C:\Windows\System32\KERNEL32.DLL (unknown line)
RtlUserThreadStart at C:\Windows\SYSTEM32\ntdll.dll (unknown line)
ERROR: Failed to precompile ProjectName [e4102d56-39a5-47ec-876b-10baf1c2b503] to C:\Users\UserName\.julia\compiled\v1.6\ProjectName\jl_14CB.tmp.
Stacktrace:
  [1] error(s::String)
    @ Base .\error.jl:33
  [2] compilecache(pkg::Base.PkgId, path::String, internal_stderr::Base.TTY, internal_stdout::Base.TTY)
    @ Base .\loading.jl:1360
  [3] compilecache(pkg::Base.PkgId, path::String)
    @ Base .\loading.jl:1306
  [4] _require(pkg::Base.PkgId)
    @ Base .\loading.jl:1021
  [5] require(uuidkey::Base.PkgId)
    @ Base .\loading.jl:914
  [6] require(into::Module, mod::Symbol)
    @ Base .\loading.jl:901
  [7] eval
    @ .\boot.jl:360 [inlined]
  [8] eval
    @ .\Base.jl:39 [inlined]
  [9] repleval(m::Module, code::Expr, #unused#::String)
    @ VSCodeServer c:\Users\UserName\.vscode\extensions\julialang.language-julia-1.2.1\scripts\packages\VSCodeServer\src\repl.jl:139
 [10] (::VSCodeServer.var"#69#71"{Module, Expr, REPL.LineEditREPL, REPL.LineEdit.Prompt})()
    @ VSCodeServer c:\Users\UserName\.vscode\extensions\julialang.language-julia-1.2.1\scripts\packages\VSCodeServer\src\repl.jl:105
 [11] with_logstate(f::Function, logstate::Any)
    @ Base.CoreLogging .\logging.jl:491
 [12] with_logger
    @ .\logging.jl:603 [inlined]
 [13] (::VSCodeServer.var"#68#70"{Module, Expr, REPL.LineEditREPL, REPL.LineEdit.Prompt})()
    @ VSCodeServer c:\Users\UserName\.vscode\extensions\julialang.language-julia-1.2.1\scripts\packages\VSCodeServer\src\repl.jl:106
 [14] #invokelatest#2
    @ .\essentials.jl:708 [inlined]
 [15] invokelatest(::Any)
    @ Base .\essentials.jl:706
 [16] macro expansion
    @ c:\Users\UserName\.vscode\extensions\julialang.language-julia-1.2.1\scripts\packages\VSCodeServer\src\eval.jl:34 [inlined]
 [17] (::VSCodeServer.var"#53#54")()
    @ VSCodeServer .\task.jl:411

```

---

<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 31, 2021, 1:34pm UTC](https://discourse.julialang.org/t/why-doesnt-work-the-module-const-ref-task-async-nothing-in-my-package/62132/2 "2021-05-31T13:34:33Z")

</div>

What you do mean by “can’t”, what did you expect and what happens?

---

<div class="post-metadata">

**Author:** ![Impressium](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/impressium/32/19575_2.png) [@Impressium](https://discourse.julialang.org/u/Impressium)\
**Post date:** [May 31, 2021, 1:41pm UTC](https://discourse.julialang.org/t/why-doesnt-work-the-module-const-ref-task-async-nothing-in-my-package/62132/3 "2021-05-31T13:41:32Z")

</div>

I updated my post above.

---

<div class="post-metadata">

**Author:** ![Impressium](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/impressium/32/19575_2.png) [@Impressium](https://discourse.julialang.org/u/Impressium)\
**Post date:** [June 1, 2021, 12:00pm UTC](https://discourse.julialang.org/t/why-doesnt-work-the-module-const-ref-task-async-nothing-in-my-package/62132/4 "2021-06-01T12:00:57Z")

</div>

> [@Impressium](#):
>
> ```julia
> module A
> const TEST = Ref{Task}(@async nothing)
> end
> 
> ```

I noticed that I could use

```julia
module A
const TEST = Ref{Any}(nothing)
end

```

instead. That worked.