Using Shift with Parameters in a subroutine

perlron has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Using Shift with Parameters in a subroutine by Anonymous Monk on Oct 20, 2014 at 09:11 UTC
perlintro#Writing subroutines, Modern Perl a loose description of how experienced and effective Perl 5 programmers work....You can learn this too. `my( $first, $second, $last ) = @_;` [download]	[reply] [d/l]
Re^2: Using Shift with Parameters in a subroutine by perlron (Pilgrim) on Oct 20, 2014 at 09:17 UTC
thanks.! :D	[reply]
Re^3: Using Shift with Parameters in a subroutine by bibliophile (Prior) on Oct 20, 2014 at 14:09 UTC
If you just want to scoop the first couple of parameters, you can do something like this: `sub f { my ($x,$y,@z) = @_; print "$x\n$y\n@z\n"; } f("first","second","third","fourth");` [download] Prints: `first second third fourth` [download]	[reply] [d/l] [select]
Re: Using Shift with Parameters in a subroutine by DanBev (Scribe) on Oct 20, 2014 at 09:18 UTC
Hi Ron, if I have correctly understood your request, you can get multiple parameters in this way `sub foo { my ($query_ref, $session_ref) = @_; }` [download] . Generally speaking, if you have 10 parameters, and you call mysub(1,2,3,4,5,6,7..10), you can take the parameters in various ways `sub mysub { my a = shift; #1 my $b = shift; #2 ... and so on` [download] `sub mysub { my @p = @_; #the array 1,2,3....10 ...` [download] and in your case `sub mysub { my ($a, $b, $c, ....$j) = @_; #$a = 1, $b = 2, ... $j = 10` [download] I hope you help.	[reply] [d/l] [select]
Re^2: Using Shift with Parameters in a subroutine by perlron (Pilgrim) on Oct 20, 2014 at 12:08 UTC
thanks DanBev. !	[reply]
Re: Using Shift with Parameters in a subroutine by Corion (Patriarch) on Oct 20, 2014 at 09:15 UTC
The new signatures are documented in perlsub since 5.20, under Signatures. The same, or a rather similar functionality can be enabled employing a source filter, but I think that the failure modes of a source-filter (introducing hard to debug syntax errors) are not really worth the nicer syntax for older Perl versions.	[reply]
Re^2: Using Shift with Parameters in a subroutine by RonW (Parson) on Oct 20, 2014 at 17:01 UTC
FYI: Method::Signatures (and a few others) don't use source filters. Instead they use the keyword API introduced in Perl 5.14.	[reply]
Re^3: Using Shift with Parameters in a subroutine by tobyink (Canon) on Oct 20, 2014 at 21:23 UTC
FYI: Method::Signatures doesn't use the keyword API introduced in Perl 5.14. Instead, it uses Devel::Declare. Ditto MooseX::Method::Signatures and Method::Signatures::Simple. Kavorka, Function::Parameters, and Fun use the Perl 5.14 keyword API. toby döt ink	[reply]
Re: Using Shift with Parameters in a subroutine by Jim (Curate) on Oct 20, 2014 at 17:12 UTC
It would only seem rational that we have a way to [condense argument passing], especially if i am passing 10 references to my subroutine. … I see there is no formal parameter support, at least in perl 5.10.1 (which is my customer version). The Perl Best Practice titled "Named Arguments" applies in the case you describe: "Use a hash of named arguments for any subroutine that has more than three parameters." This Best Practice is in Chapter 9, Subroutines, which is available online here: http://oreilly.com/catalog/perlbp/chapter/ch09.pdf. "Named Arguments" is on pp. 182-3.	[reply]
Re^2: Using Shift with Parameters in a subroutine by perlron (Pilgrim) on Oct 21, 2014 at 17:30 UTC
thanks Jim. that's definitely a case in point then.	[reply]
Re: Using Shift with Parameters in a subroutine by Anonymous Monk on Oct 20, 2014 at 09:17 UTC
heard we have subroutine signature support in perl5.20. if so can you point me to the man pages for that ? https://metacpan.org/pod/distribution/perl/pod/perl5200delta.pod#Experimental-Subroutine-signatures https://metacpan.org/pod/perlsub#Signatures Sub::Signatures, Sub::MicroSig, Sub::NamedParams/Params::Named/Method::Signatures... perldeltas - every perl*delta in one file with each version properly linkable .	[reply]
Re: Using Shift with Parameters in a subroutine by Marshall (Canon) on Oct 21, 2014 at 20:42 UTC
It appears to me that you are only passing 2 refs to the sub. `sub foo{ my ($query_ref, $session_ref) = @_; }` [download] These refs should be references to hash tables. In general, passing 10 parameters to a sub is not a good idea. Better is reference to a hash.	[reply] [d/l]
Re^2: Using Shift with Parameters in a subroutine by capstan (Novice) on Oct 23, 2014 at 16:34 UTC
Just to be thorough, `my ($one, $two) = _@;` works once, but ignores the side effect of shift (removing the arguments from the @_ array). As Marshall says, using a reference to an array would be the best way to deal with a lot of parameters, but if you wanted to, say, process two at a time, you could do `while (my ($one,$two) = splice @_, 0, 2) { #do something }` [download] (you'll get an uninitialized value warning if you supply an odd number of parameters)	[reply] [d/l] [select]
Re^3: Using Shift with Parameters in a subroutine by perlron (Pilgrim) on Oct 25, 2014 at 17:59 UTC
thanks. i didnt realise this earlier, about the impact on @_ . Do not wait to strike when the iron is hot! Make it hot by striking - WB Yeats	[reply]
Re^2: Using Shift with Parameters in a subroutine by perlron (Pilgrim) on Oct 22, 2014 at 08:27 UTC
ok. ill improvise then. thanks. the 10 parameters was purely hypothetical , as a programming possibility. thats all.	[reply]