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Re^3: is my api wrapper abstraction ok (is it perlish?)

by tobyink (Abbot)
on Jan 19, 2013 at 11:24 UTC ( #1014197=note: print w/replies, xml ) Need Help??

in reply to Re^2: is my api wrapper abstraction ok (is it perlish?)
in thread is my api wrapper abstraction ok (is it perlish?)

*answer_comments is a glob - basically an entry in Perl's symbol table. It is kind of a bundle which contains sub answer_comments, our $answer_comments, our @answer_comments, our %answer_comments and the answer_comments bareword file handle.

If you assign one glob to another, like *xxx = *yyy, then it makes sub xxx and sub yyy aliases for each other, and our $xxx and our $yyy aliases for each other, etc.

use 5.010; use strict; use warnings; our ($xxx, $yyy, @xxx, @yyy); *xxx = *yyy; # alias $xxx = 42; say $yyy; # says "42" @xxx = (9,9,9); say "@yyy"; # says "9 9 9"

Anyway, that's what happens when you assign one glob to another glob. But you can also assign references to a glob, in which is doesn't alias the whole bundle, but just the relevant slot within the glob. For example:

use 5.010; use strict; use warnings; our ($xxx, $yyy, @xxx, @yyy); *xxx = \$yyy; # alias $yyy, but not @yyy $xxx = 42; say $yyy; # says "42" @xxx = (9,9,9); say "@yyy"; # says nothing

And so one_param returns a coderef, and we can assign it to the glob:

*answers_comments = one_param("answers","comments");

This effectively installs the sub into the package with a given name. Almost as if you'd done:

package ...; sub answers_comments { ...; }

(This is what Exporter does internally - that module is not as magic as it seems.)

I say "almost" though. There's one key difference, and that's what the CPAN module Sub::Name takes care of. When the answers_comments method is called, Perl still internally treats it as an anonymous coderef. Which means that stack traces (e.g. Carp) would show it as "__ANON__" rather than "answers_comments".

Naming the sub is also important if you use something like namespace::autoclean which deletes subs it finds in your package that don't look like methods. Naming a sub makes it look like a method.

So Sub::Name is well worth using when you muck around with globs; it's a shame it's not bundled with Perl.

perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

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Re^4: is my api wrapper abstraction ok (is it perlish?)
by gideondsouza (Pilgrim) on Jan 19, 2013 at 13:51 UTC

    Thanks a lot for your explanation. I really appreciate it :)

    Sub::Name, on cpan has a 4 open bugs, I looked through them and I'm assuming that it should be ok to use it if I were distributing my wrapper as a module?

      Obviously it's up to you to judge whether it's suitably stable, but Moose and DBIx::Class both use Sub::Name, so personally I'd consider it to be pretty reliable.

      perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'

        Thanks. That more than convinces me

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