Check if list of variables are defined

General Usage
1

Hi all,

I’m trying to determine if a user has defined all the necessary input variables. I’d like to store the variable names in a list (either a tuple or array) and then be able to cycle through it and check if they’re defined. This seems like it should be simple, but I can’t get the syntax right. I tried various things such as the following, but I get errors like the one below. Any suggestions?

julia> a = 1
1

julia> vlist = (:a, :b)
(:a, :b)

julia> @isdefined(vlist[1])
ERROR: LoadError: MethodError: no method matching var"@isdefined"(::LineNumberNode, ::Module, ::Expr)
Closest candidates are:
  var"@isdefined"(::LineNumberNode, ::Module, ::Symbol) at /Applications/Julia-1.7.app/Contents/Resources/julia/share/julia/base/essentials.jl:150
in expression starting at REPL[58]:1
2 
julia> isdefined.(Ref(Main), vlist)
(true, false)
3

You can use isdefined(@__MODULE__, vlist[1]) instead. I’d encourage you to find a different way to structure your code though; this pattern isn’t (usually) a good idea.

4

So if I do what @nilshg suggested I get the right results, but I get the following with what @pfitzseb suggested, which seems weird as this is pretty much the same thing:

julia> a
1

julia> b
2

julia> c
ERROR: UndefVarError: c not defined

julia> d
ERROR: UndefVarError: d not defined

julia> isdefined.(Ref(Main), vlist)
(true, true, false, false)

julia> isdefined(Ref(Main), vlist[1])
false

julia> isdefined(Ref(Main), vlist[2])
false

julia> isdefined(Ref(Main), vlist[3])
false

julia> isdefined(Ref(Main), vlist[4])
false
5

That’s not what I wrote though. You have an extraneous Ref in there.

6

My apologies… was thinking those would both be pointing to the same thing for the example in the REPL. Yes, they both work fine.

@pfitzseb what exactly is the @MODULE doing?

7 
help?> @__MODULE__
  @__MODULE__ -> Module

  Get the Module of the toplevel eval, which is the Module code is currently
  being read from.

Generally, Ref(x) != x; when broadcasting, the Ref “unwrapped”.