Running this code
module mod1
export foo
function foo()
i=0
for ii in 1:10
global i+=ii
end
i
end
end
mod1.foo()
gives UndefVarError: i not defined.
It seems that the way to do it is by adding a global before the variable i:
module mod2
export bar
function bar()
global i=0
for ii in 1:10
global i+=ii
end
i
end
end
mod2.bar()
This gives: 55
Why does the first method not work? As I understand the for introduces a new scope. Therefore I need the global inside the loop. But why do I also need it outside of the loop?
(I am using julia 1.5.0)
The correct way to write this would be:
module mod1
export foo
function foo()
i=0
for ii in 1:10
i+=ii
end
i
end
end
julia> mod1.foo()
55
There are 3 scopes introduced here (from outermost to innermost):
mod1foofor bodyThe rules for scoping are explained in the manual. In this particular case: when i is referred to in the for body, we first look for a variable named i defined in that same scope. Since none is found, we look for it in the enclosing scope which is the local scope of foo... and find the variable declared using i=0.
If no variable named i had been found in the local foo scope, we'd have had to look into the enclosing scope, which is a global scope. And in this case, you'd have had to put the global keyword to explicitly allow it (because it has performance implications).
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