> I would be ok with loop variables always being local to the loop so that
> this would happen:
>
> julia> i = 0
> 0
>
> julia> for i = 1:5
> println(i)
> end
> 1
> 2
> 3
> 4
> 5
>
> julia> i
> 0
>
>
> That would simplify the semantics of for loops at the cost of making it
> harder to access the final value of a loop variable – but that's a somewhat
> rare thing to do and explicitly assigning the loop variable to an variable
> from outside the loop is arguably clearer.
I find the scoping rules complex. I think this might make them a tad
less complex as the rules for comprehensions and for-loops become
identical (right?). Also it would be more similar to functions, their
arguments also being local.
If the loop variable is needed then this would work
iout = 1
for i = 1:5
println(i)
if i==something
iout = i
end
end
> On Fri, Feb 6, 2015 at 7:05 AM, David Higgins <[email protected]>
> wrote:
>
>> So all of this seems to be a result of the for loop basically using a
>> range/array type variable on the right hand side of the loop variable. So
>> even if I change the value of the iterator variable within the loop I
>> cannot change the array over which I am looping (anyone used to Python will
>> find this natural, I'm more used to C).
>>
>> I guess everything is consistent now.
>>
>> David
>>
>> On Friday, 6 February 2015 12:25:34 UTC+1, David Higgins wrote:
>>
>>> I have a use case I found interesting. I guess it's well known to some of
>>> you, but I never noticed it in the documentation and I find it
>>> counterintuitive, both as an experienced programmer and with respect to the
>>> typical scope rules of variables in Julia.
>>>
>>> I accidentally nested a loop within another loop using the same index
>>> variable for both loops. First of all, there are reasons sometimes you'd
>>> want to do this but I did it by accident as a typo. But the scope rules of
>>> variables for Julia, as applied to functions, state that you can read a
>>> variable value at a lower level in the hierarchy but you cannot write to it
>>> so I actually assumed that this also applied to loops (*first mistake*).
>>>
>>> Secondly, as you'll see if you execute the simplified example of what I
>>> actually did here:
>>> for i = 1:5
>>> for j = 1:5
>>> for i = 1:3
>>> print("tick ");
>>> end
>>> print(" $i\n");
>>> end
>>> print(" $j $i\n");
>>>
>>> Julia still knew to only run the outer loop 5 times, despite the fact
>>> that I was setting the variable bound to $i at level 2 to the value 3 at
>>> level 3 in the nested hierarchy of loops. I suspect that I can see what's
>>> happening at the compiler/interpretter level, but I do think that this is
>>> confusing.
>>>
>>> We seem to have the worst of both worlds here in that we can access and
>>> change $i at an inner loop level and have the change be persistent, but yet
>>> we cannot change the behaviour of the outer loop (as would be the case in
>>> C).
>>>
>>> What do you guys think? Can this be clarified in the documentation, or
>>> should the actual behaviour of julia be modified?
>>>
>>> David.
>>>
>>
