CODEWITHSUNDEEP
julia
Steven Siew
Steven Siew

Reputation: 873

How variable behave in for loop have changed

Consider this source code

println("Julia language version ",VERSION)
i=666
for i = 1:2
    println("i is $i")
end
println("global i is $i")

function main()
    j = 666
    for j = 1:2
        println("j is $j")
    end
    println("global j is $j")
end

main()

Consider the output of version 0.6

Julia language version 0.6.3
i is 1
i is 2
global i is 2
j is 1
j is 2
global j is 2

Compare to the output of version 1.0

Julia language version 1.0.0
i is 1
i is 2
global i is 666
j is 1
j is 2
global j is 666

I can't change the value of variable i and variable j using a for loop like I can before in version 0.6

I think C programmers will have the shock of their lives...

Upvotes: 1

Views: 222

Answers (1)

laborg
laborg

Reputation: 871

If you use Julia 0.7 (which is basically == 1.0 with deprecations) you would see the necessary deprecation messages for the intended behaviour change:

┌ Warning: Deprecated syntax `implicit assignment to global variable `i``.
│ Use `global i` instead.
└ @ none:0
┌ Warning: Loop variable `i` overwrites a variable in an enclosing scope. In the future the variable will be local to the loop instead.
└ @ none:0
i is 1
i is 2
global i is 2

So to get what you want you could write:

function main()
    global j = 666
    for j = 1:2
        println("j is $j")
    end
    println("global j is $j")
end

main()

Your first example on the global level should theoretically be dealt with using for outer i.. as described in https://docs.julialang.org/en/latest/manual/variables-and-scoping/#For-Loops-and-Comprehensions-1 but currently this is not handled in the REPL. See this issue: https://github.com/JuliaLang/julia/issues/24293

Upvotes: 4

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