multiple local vars in a foreach loop

[shawnkielty]

Hello ... i am pretty new to perl -- I have a array that is a series of key value pairs What I want to do is a foreach loop through the array -- something like this:

my %hash; 

foreach $key $value (@keys) {
    $hash($key) = $value;
}

Is this possible? Or do i just not understand the syntax?

[LanX]

The simple answer

my %hash=@keys;

already does what you want. =)

UPDATES

The long answer!

Regarding your initial question: "unfortunately not"!

Perl5 doesn't provide a built-in way to have multiple loop vars in foreach.

There are several workarounds with while loops:

• destructive with splice or multiple shifts

• iterator with List::MoreUtils::natatime() or pairwise()

• classic with c-stile for with two index-increments per iteration

but these workarounds have been discussed so often in the monastery that I'd prefer to link them after finding them.

Splice

In this case (ignoring the solution on top) I would do something with splice:

  DB<113> @array = (a =>1,b=>2)
 => ("a", 1, "b", 2)

  DB<114> while ( my ($key,$val) = splice(@array,0,2) ) {
           $hash{$key}=$val;
          }

  DB<115> \%hash
 => { a => 1, b => 2 }

  DB<116> \@array            # emptied! 
 => []

You need to copy @array in case I wanna keep the initial elements after the loop.

Older discussions

googling the monastery for splice+natatime

Errata

Originally I proposed this code

while(@array) {
   $hash{shift @array} = shift @array;
}

But I was bitten by precedence, the code does it the wrong way around:

  DB<108> @array = ( a => 1, b => 2 )
 => ("a", 1, "b", 2)

  DB<109> $hash{shift @array} =shift @array while @array

  DB<110> \%hash
 => { 1 => "a", 2 => "b" }

[roboticus]

shawnkielty:

Update: LanX is (of course) correct.

Not with foreach, but you can do it using while and each:

my %hash;

while (my ($key, $value) = each %hash) {
   ...
}

...roboticus

When your only tool is a hammer, all problems look like your thumb.

[LanX]

Right answer to wrong question! ;-)

  DB<156> while (my ($key, $value) = each @a) { print "$key, $value" }
+;;
Type of arg 1 to each must be hash (not array dereference) at (eval 13
+5)[multi_perl5db.pl:644] line 2, near "@a) "

[choroba]

Depends on the version of Perl: each.