# Passing symbol values using \`@everywhere\`?

**URL:** <https://discourse.julialang.org/t/passing-symbol-values-using-everywhere/43178>\
**Category:** General Usage\
**Tags:** parallel, distributed\
**Created:** [July 16, 2020, 1:37pm UTC](https://discourse.julialang.org/t/passing-symbol-values-using-everywhere/43178 "2020-07-16T13:37:37Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![haberdashPI](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/haberdashpi/32/26337_2.png) [@haberdashPI](https://discourse.julialang.org/u/haberdashPI)\
**Post date:** [July 16, 2020, 1:37pm UTC](https://discourse.julialang.org/t/passing-symbol-values-using-everywhere/43178/1 "2020-07-16T13:37:37Z")

</div>

This seems like a bug:

```julia
julia> using Distributed; addprocs()
julia> classifier = :logistic_l1
julia> @everywhere classifier = $classifier
ERROR: On worker 2:
UndefVarError: logistic_l1 not defined
top-level scope at none:0
eval at ./boot.jl:331
#101 at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.4/Distributed/src/process_messages.jl:290
run_work_thunk at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.4/Distributed/src/process_messages.jl:79
run_work_thunk at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.4/Distributed/src/process_messages.jl:88
#94 at ./task.jl:358

...and 16 more exception(s).

Stacktrace:
 [1] sync_end(::Array{Any,1}) at ./task.jl:316
 [2] macro expansion at ./task.jl:335 [inlined]
 [3] remotecall_eval(::Module, ::Array{Int64,1}, ::Expr) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.4/Distributed/src/macros.jl:217
 [4] top-level scope at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.4/Distributed/src/macros.jl:201
 [5] eval(::Module, ::Any) at ./boot.jl:331
 [6] eval_user_input(::Any, ::REPL.REPLBackend) at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.4/REPL/src/REPL.jl:86
 [7] run_backend(::REPL.REPLBackend) at /home/davidlittle/.julia/packages/Revise/tV8FE/src/Revise.jl:1165
 [8] top-level scope at none:0

```

My current workaround is to just convert to a symbol on the worker, like so.

```julia
julia> @everywhere classifier = Symbol($(string(classifier)))

```

Is this expected behavior?

---

<div class="post-metadata">

**Author:** ![oheil](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oheil/32/220745_2.png) [@oheil](https://discourse.julialang.org/u/oheil)\
**Post date:** [July 16, 2020, 8:49pm UTC](https://discourse.julialang.org/t/passing-symbol-values-using-everywhere/43178/2 "2020-07-16T20:49:12Z")

</div>

Actually I like your workaround, but how about

```julia
julia> using Distributed; addprocs()

julia> classifier = :logistic_l1

julia> @everywhere classifier = $(QuoteNode(classifier))

julia> @everywhere println(typeof(classifier))
Symbol
      From worker 9: Symbol
      From worker 3: Symbol
      From worker 8: Symbol
      From worker 7: Symbol
      From worker 4: Symbol
      From worker 10: Symbol
      From worker 2: Symbol
      From worker 14: Symbol
      From worker 11: Symbol
      From worker 5: Symbol
      From worker 12: Symbol
      From worker 6: Symbol
      From worker 15: Symbol
      From worker 13: Symbol

```

Is this less workaround? I don’t know.

---

<div class="post-metadata">

**Author:** ![haberdashPI](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/haberdashpi/32/26337_2.png) [@haberdashPI](https://discourse.julialang.org/u/haberdashPI)\
**Post date:** [July 16, 2020, 8:57pm UTC](https://discourse.julialang.org/t/passing-symbol-values-using-everywhere/43178/3 "2020-07-16T20:57:59Z")

</div>

Seems like a matter of taste: my personal choice would be to avoid `QuoteNode`; I think the `Symbol($(string(classifier))` construct is likely to be more transparent to more people.

---

<div class="post-metadata">

**Author:** ![oheil](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oheil/32/220745_2.png) [@oheil](https://discourse.julialang.org/u/oheil)\
**Post date:** [July 16, 2020, 9:05pm UTC](https://discourse.julialang.org/t/passing-symbol-values-using-everywhere/43178/4 "2020-07-16T21:05:19Z")

</div>

Yes, thats what I thought too. Your “workaround” is easy to understand, but uses some more CPU on the workers. QuoteNote should be no cost at the workers. So it depends on the real problem to solve.  
Actually it is not quite clear to me why

```julia
julia> :(@everywhere classifier = $(QuoteNode(classifier)))
:(#= REPL[13]:1 =# @everywhere classifier = :logistic_l1)

```

but

```julia
julia> :(@everywhere classifier = $classifier)
:(#= REPL[16]:1 =# @everywhere classifier = logistic_l1)

```

I think to understand this we have to look into the code of interpolation (but I prefer to go to bed now. Good night 😴).