Loop (i, j) without zip() stopped at the 2nd round

[Sukera]

@JiuuJulia

Do you mean tuple (i, j) first points to the first two letters in a, and then points to the first two letters in b? (It took a while for me to make it clear in my mind )

Yes, exactly.

@JiuuJulia

I wonder what “state” means here, does it mean the depth or the length of the tuple used for iteration? (e.g. in this case length of (i,j)is 2)

The iteration state is something that is passed to the next time iterate is called - it’s specific to each iterable. In the case of a tuple, it’s just the index of the next element in the tuple.

julia> a = "AAAGCTAGCTAGCTAGACT"
"AAAGCTAGCTAGCTAGACT"

julia> b = "ATAGCTAGCCAGCTAAACT"
"ATAGCTAGCCAGCTAAACT"

julia> tup = (a,b)
("AAAGCTAGCTAGCTAGACT", "ATAGCTAGCCAGCTAAACT")

julia> iterate(tup)
("AAAGCTAGCTAGCTAGACT", 2)

julia> iterate(tup, 2)
("ATAGCTAGCCAGCTAAACT", 3)

julia> iterate(tup, 3) # returns `nothing`, indicating the end of the iteration

The iteration state is arbitrary though, so it can be anything you’d like it to be for your own type.

@JiuuJulia

Cause when I create a long tuple, it worked.

Yes. You’re literally creating a tuple of three strings by writing (a,b,c). Since loops have their own scope, your loop variable str shadows the existing str variable outside of the loop. So the str in your loop first is a, then b, then c.