Scalar References - oxymoron?
Reading http://perldoc.perl.org/perlreftut.html I see it’s possible to create a scalar reference. What situation would require someone to create a reference to a scalar? I thought refs were only useful for passing complex data structures. Is it just because Perl lets you, or is there a reason I’m not aware of? It seems like it would just be redundant. Thanks, Frank -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: Scalar References - oxymoron?
On 04/03/2017 06:52 PM, SSC_perl wrote: Reading http://perldoc.perl.org/perlreftut.html I see it’s possible to create a scalar reference. What situation would require someone to create a reference to a scalar? I thought refs were only useful for passing complex data structures. Is it just because Perl lets you, or is there a reason I’m not aware of? It seems like it would just be redundant. i have used them for efficiency when passing large strings or buffers. perl will copy a scalar onto the stack when passing into or back from a sub. passing a scalar ref is cheap (just a single SV with a pointer for its value in internals parlance). that is one use and there are others. not as common as using refs for arrays and hashes but it definitely can be useful for scalars. uri -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: Scalar References - oxymoron?
On Mon, 03 Apr 2017 15:52:59 -0700, SSC_perl wrote: > Reading http://perldoc.perl.org/perlreftut.html I see it’s possible to > create a scalar reference. What situation would require someone to > create a reference to a scalar? I thought refs were only useful for > passing complex data structures. Is it just because Perl lets you, or > is there a reason I’m not aware of? It seems like it would just be > redundant. They can make handy objects, whivh have to be references, but if you're making an inside-out object which doesn't contain its own attributes, you want something light and immutable. -- Peter Scott http://www.perlmedic.com/ http://www.perldebugged.com/ http://www.informit.com/store/product.aspx?isbn=9780133036268 -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
Re: Scalar References - oxymoron?
On Mon, Apr 3, 2017 at 6:55 PM SSC_perl wrote: > Reading http://perldoc.perl.org/perlreftut.html I see it’s > possible to create a scalar reference. What situation would require > someone to create a reference to a scalar? I thought refs were only useful > for passing complex data structures. Is it just because Perl lets you, or > is there a reason I’m not aware of? It seems like it would just be > redundant. It is mostly used to avoid copying large amounts of data. If you are using Perl 5.20.0 or newer, this is not necessary as long as you aren't changing the data as strings are now COW (copy-on-write). Prior to Perl 5.20.0 if you had code like: my $big = "a" x (1024*1024*1024); # a gigabyte of 'a's sub foo ( my $arg = shift; ); foo($big) then it had to copy the whole gigabyte into a new string. If this was something you expected, you could (and probably still should if you need to modify the string) say sub foo ( my $ref = shift; # do stuff with $$ref ); and that would not create a copy. Other uses include * flyweight/inside-out objects: http://www.perl.com/pub/2003/06/13/design1.html#flyweight * Signaling/metadata (eg the open function will open an in-memory file if passed a scalar ref of the file's contents) * in/out function parameters without having to use the clunky $_[index] aliasing (not recommended, really only useful in languages that don't have multiple return values) * storing the same scalar in more than data structure (warning this can lead to spooky-action-at-a-distance bugs)
Re: Scalar References - oxymoron?
Thanks for all the replies. It’s been a very interesting thread. Frank -- To unsubscribe, e-mail: beginners-unsubscr...@perl.org For additional commands, e-mail: beginners-h...@perl.org http://learn.perl.org/
