Local variable inside a loop: why it ERRORs

New to Julia
2

It always helps to form a minimal reproducible example. Get rid of all unnecessary lines so you can focus on the underlying issue.

Here’s one example:

julia> function test()
           for i in 1:2
               local item
               if i == 1
                   item = [i]
               else
                   item[] += 1
               end
           end
       end
test (generic function with 2 methods)

julia> test()
ERROR: UndefVarError: `item` not defined in local scope
Suggestion: check for an assignment to a local variable that shadows a global of the same name.
Stacktrace:

One the first iteration, you declare local item and initialise it.

On the second iteration, you declare a new local item, and then attempt item[] += 1, which tries to read item[]. But because of local item, the variable does not persist between iterations and so it doesn’t exist in iteration 2.

Change where you put the local:

julia> function test()
           local item
           for i in 1:2
               if i == 1
                   item = [i]
               else
                   item[] += 1
               end
           end
           return item
       end
test (generic function with 2 methods)

julia> test()
1-element Vector{Int64}:
 2
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