UndefRefError: access to undefined reference, how to fix the following error?

General Usage
1

I’m running some Julia code and the error message I get is as the following:

UndefRefError: access to undefined reference
   in top-level scope at base/None
   in simulate! at do_sim.jl:10
   #simulate!#46 at so_sim.jl:38
   simulateNextEvent! at do_sim.jl:84
   simulateEvent! at do_sim.jl:184
   findAmbToCallReturnRouteDistTime! at decisions.jl:117
   get property at base/sysing.jl:18

Yet, I have checked the code several times and it should be good. Any comments about where and how to fix the error here?

2

Here’s one way that such an error can get thrown:

julia> r = Ref{Any}()
Base.RefValue{Any}(#undef)

julia> r[]
ERROR: UndefRefError: access to undefined reference

Somewhere in your code you’re trying to access a reference that was initialized as undef and never set. Impossible to say more without the code itself.

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3

What is Ref by the way?

4

It’s just a box that can hold something — and what it is holding onto can change.

https://docs.julialang.org/en/v1/base/c/#Core.Ref

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