Importing functions into packages

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

Looking at code in pmd_grapher in the CPAN Module::Dependency I find the following:

use strict;
use Module::Dependency::Grapher;
*Module::Dependency::Grapher::TRACE = \*TRACE;
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I'm puzzled by the use of globs here. Examining the code shows that only &TRACE is used, not %TRACE, $TRACE or @TRACE. I would have expected to see

use strict;
use Module::Dependency::Grapher qw(&TRACE);
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Is there something fancy the author is doing with globs here? Is there some practical difference?

Comment on Importing functions into packages - globs vs use Select or Download Code

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Re: Importing functions into packages - globs vs use by davorg (Chancellor) on Nov 30, 2006 at 16:42 UTC
They're doing different things. The first one takes the TRACE glob from the current package and installs a reference to it into the Module::Dependency::Grapher package. This effectively pushes your TRACE subroutine (and other objects) into the Module::Dependency::Grapher package. The second one imports the TRACE subroutine from Module::Dependency::Grapher into the current package (assuming that Module::Dependency::Grapher is using Exporter). So they are the complete opposite of each other. -- <http://dave.org.uk> "The first rule of Perl club is you do not talk about Perl club." -- Chip Salzenberg	[reply]
Re^2: Importing functions into packages - globs vs use by throop (Chaplain) on Nov 30, 2006 at 16:53 UTC
Ahhh! many thanks. That explains some other strange-seeming behavior that I was not figuring out myself. And sheds light on why &Module::Dependency::Grapher::TRACE was defined, but as a no-op.	[reply]
Re^3: Importing functions into packages - globs vs use by ikegami (Patriarch) on Nov 30, 2006 at 16:55 UTC
Doing the whole glob (instead of overwriting the CODE slot) prevents a 'redefined' warning, ( ~~I think.~~ Confirmed. )	[reply]
Re: Importing functions into packages - globs vs use by themage (Friar) on Nov 30, 2006 at 16:42 UTC
hi throop, The author is doing exactly the oposite to what you are expecting. What that code do is redefine the sub TRACE in Module::Dependency::Grapher with the one in your local scope. After this code, every call made to TRACE inside Module::Dependency::Grapher will call your local TRACE, not the original one defined in Module::Dependency::Grapher. Using `use Module::Dependency::Grapher qw(TRACE);` you import Module::Dependency::Grapher::TRACE to your local scope, that can then be called with TRACE(...). TheMage Talking Web	[reply] [d/l]
Re: Importing functions into packages - globs vs use by brian_d_foy (Abbot) on Dec 01, 2006 at 09:34 UTC
That code is doing a little bit of black magic to replace part of a module without changing the module source. I talk about that the Dynamic Subroutines chapter of Mastering Perl (and it shows up in a few other chapters too). It can be a very handy way to fix a module and not see your changes disappear when an admin updates the module. -- brian d foy <brian@stonehenge.com> Subscribe to The Perl Review	[reply]