Passing several arguments

[Jan Eden]

Hi all,

I have a subroutine which fills into several hashes and arrays (%author_indexlines, %poem_lines, @alphabet_index etc). How can I return those variables and pass them to another subroutine? This does not work, of course

sub read_index {
blablabla
return (%author_indexlines, %poem_lines, @alphabet_index);
}

sub write_index {
my (%author_indexlines, %poem_lines, @alphabet_index) = shift;
blablabla
}

write_index(&read_index);

I thought that this might be achieved returning references to the respective arrays and hashes and dereference them after passing, but since the elements have local scope in the read_index sub, I am not sure if this might work:

sub read_index {
blablabla
return (\%author_indexlines, \%poem_lines, \@alphabet_index);
}

sub write_index {
my ($author_ref, $poem_ref, $alphabet_ref) = shift;
my @author_index = @$author_ref;
blablabla
}

Any hints appreciated,

Jan
--
These are my principles and if you don't like them... well, I have others. - Groucho Marx

[Wiggins D'Anconia]

Jan Eden wrote:

> Hi all,
>
> I have a subroutine which fills into several hashes and arrays (%author_indexlines, %poem_lines, @alphabet_index etc). How can I return those variables and pass them to another subroutine? This does not work, of course
>
> sub read_index {
> blablabla
> return (%author_indexlines, %poem_lines, @alphabet_index);
> }
>
> sub write_index {
> my (%author_indexlines, %poem_lines, @alphabet_index) = shift;
> blablabla
> }
>
> write_index(&read_index);
>
> I thought that this might be achieved returning references to the respective arrays and hashes and dereference them after passing, but since the elements have local scope in the read_index sub, I am not sure if this might work:
>
> sub read_index {
> blablabla
> return (\%author_indexlines, \%poem_lines, \@alphabet_index);
> }
>
> sub write_index {
> my ($author_ref, $poem_ref, $alphabet_ref) = shift;
> my @author_index = @$author_ref;
> blablabla
> }
>
> Any hints appreciated,
>

"Not sure if it might work"... did you try? Trial and error is the best
way to learn....

perldoc perlreftut
perldoc perlref
perldoc perldsc
perldoc perllol

Until you have a strong grasp of references make heavy use of
Data::Dumper it is your friend and will help you wrangle more complex
structures.

May I also suggest to improve your understanding of scoping issues:

[url]http://perl.plover.com/FAQs/Namespaces.html[/url]

[url]http://danconia.org[/url]

[Drieux]

On Jan 27, 2004, at 3:26 AM, Jan Eden wrote:
[..]

> I have a subroutine which fills into several hashes and arrays
> (%author_indexlines, %poem_lines, @alphabet_index etc). How can I
> return those variables and pass them to another subroutine? This does
> not work, of course

[..]

perldoc -q "How can I pass/return a {Function, FileHandle, Array,"

remember that your core signature is

my @return_list = function(@arglist);

so the only way that you can return more than one
array or hash will be by passing their refs

my ($auther, $poem, $index) = function(@arglist);
....

sub function {
....
(\%author_indexlines, \%poem_lines, \@alphabet_index, $etc)
}

then you re-ref them as

while( my ($k,$v) = each %$author )
{
....
}

ciao
drieux

---

[Jeff 'Japhy' Pinyan]

On Jan 27, Jan Eden said:

>I have a subroutine which fills into several hashes and arrays
>(%author_indexlines, %poem_lines, @alphabet_index etc). How can I return
>those variables and pass them to another subroutine? This does not work,
>of course
>
>sub read_index {
> blablabla
> return (%author_indexlines, %poem_lines, @alphabet_index);
> }

You most CERTAINLY want to return references to those.

sub read_index {
...
return \(%author_indexlines, %poem_lines, @alphabet_index);
}

That last line is equivalent to

return (\%author_indexlines, \%poem_lines, \@alphabet_index);

> sub write_index {
> my (%author_indexlines, %poem_lines, @alphabet_index) = shift;
>}

That is just pure nonsense. First of all, shift() only returns ONE
element from an array. Second, you can't assign to multiple aggregates at
once (aggregates meaning arrays and hashes). You'll need to use
references here too:

sub write_index {
my ($authref, $poemref, $alpharef) = @_;
my %author_indexlines = %$authref;
my %poem_lines = %$poemref;
my @alphabet_index = @$alpharef;
...
}

>I thought that this might be achieved returning references to the
>respective arrays and hashes and dereference them after passing, but
>since the elements have local scope in the read_index sub, I am not sure
>if this might work:

You guessed almost correctly. You still have 'shift', though. shift()
will only return ONE element. Getting all of them from @_ is the way to
do it.

--
Jeff "japhy" Pinyan [email]japhy@pobox.com[/email] [url]http://www.pobox.com/~japhy/[/url]
RPI Acacia brother #734 [url]http://www.perlmonks.org/[/url] [url]http://www.cpan.org/[/url]
<stu> what does y/// stand for? <tenderpuss> why, yansliterate of course.
[ I'm looking for programming work. If you like my work, let me know. ]

[Jan Eden]

Jeff 'japhy' Pinyan wrote:

>On Jan 27, Jan Eden said:
>

>>I have a subroutine which fills into several hashes and arrays
>>(%author_indexlines, %poem_lines, @alphabet_index etc). How can I
>>return those variables and pass them to another subroutine?

[snip]

>>I thought that this might be achieved returning references to the
>>respective arrays and hashes and dereference them after passing,
>>but since the elements have local scope in the read_index sub, I am
>>not sure if this might work:

>
>You guessed almost correctly. You still have 'shift', though.
>shift() will only return ONE element. Getting all of them from @_
>is the way to do it.
>

Ok. I noticed this problem trying to get it to work and did not rethink theway shift works. Thanks!

- Jan
--
There's no place like ~/