Re^4: why each/keys/values can't work on slice? (updated)

use feature qw/say/;
my @bb = 1..10; 
while(my ($ind, $val) = each @bb){
    say "ind is $ind";
           if($ind >5){
                while(my ($inner_ind, $inner_val) = each @bb){
                   say "inner ind is $inner_ind, inner val is $inner_v
+al"
        }
    }
}

# will endless loop since while share one iterator

while(my ($ind, $val) = each @bb){
    say "ind is $ind";
}
# this will quit loop successfully.
[download]

I don't understand why every array has to have only one iterator, please enlighten me. and guess each/keys doesn't work on slice would be relative to this reason?

Comment on Re^4: why each/keys/values can't work on slice? (updated) Download Code

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Re^5: why each/keys/values can't work on slice? (updated) by LanX (Saint) on Jan 11, 2023 at 05:45 UTC
> > maybe show us an example from another language w/o "this limitation" to learn from? :) these are not examples from another language demonstrating no "limitations"... :) anyway in Perl 5.36 you can do this `use v5.36; use warnings; use experimental qw/for_list/; my %hash; @hash{"a".."e"} = 1..5; for my ($key, $value) ( %hash{"c","a","e"} ) { say "$key -> $value"; }` [download] `$ perl /d/perl/pm/iterate_hash_slice.pl c -> 3 a -> 1 e -> 5` [download] Cheers Rolf _{(addicted to the 𐍀𐌴𐍂𐌻 Programming Language :) Wikisyntax for the Monastery}	[reply] [d/l] [select]
Re^5: why each/keys/values can't work on slice? (updated) by ikegami (Patriarch) on Jan 11, 2023 at 19:07 UTC
I don't understand why every array has to have only one iterator First of all, it's one more than needed. `for my $ind ( 0 .. $#bb ) { say "ind is $ind"; }` [download] And to answer your question, it's the maximum you can have. If you want multiple iterators, they necessarily have to be external to the array. For example, in C#, you have to create an external iterator. `using ( var enumerator = list.GetEnumerator() ) { while ( enumerator.MoveNext() ) { var item = emumerator.current; // ... } }` [download] Nothing stops you from doing the same in Perl. Now, C# does have syntactical sugar that makes this cleaner. `for ( var item in list ) { // ... }` [download] Again, nothing stops you from doing the same in Perl. If no one's done it, I guess it's not that useful. (I'm not saying noone's done it. I have no idea.)	[reply] [d/l] [select]