How to check if a function exists within a package?

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

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Re: How to check if a function exists within a package? by ikegami (Patriarch) on Sep 08, 2008 at 01:06 UTC
For functions, `defined`. `if ( defined( &perlmonk::funnyfunction ) )` [download] For methods, `can`. Checks inheritance. `if ( perlmonk->can('funnyfunction') )` [download] `if ( $obj->can('funnyfunction') )` [download]	[reply] [d/l] [select]
Re^2: How to check if a function exists within a package? by jettero (Monsignor) on Sep 08, 2008 at 02:01 UTC
`if ( defined( &perlmonk::funnyfunction ) )` Why wouldn't that call the function passing in @_ and check defined on the result? I mean, I see that it doesn't do that, but why? You have to put the ()'s on the end of it to get what I'd expect. -Paul	[reply] [d/l]
Re^3: How to check if a function exists within a package? by ikegami (Patriarch) on Sep 08, 2008 at 02:11 UTC
It's just another special parsing rule. `exists` and `goto` are exactly the same, but they are hardly the only three functions that have special parsing rules. `map`'s curlies don't create a hash. `print`'s file handle isn't a function name. And the list goes on.	[reply] [d/l] [select]
Re^2: How to check if a function exists within a package? by rapide (Beadle) on Sep 08, 2008 at 01:38 UTC
Great answer. Since I had methods it was the right answer to use can. Thanks everyone!	[reply]
Re: How to check if a function exists within a package? by GrandFather (Saint) on Sep 08, 2008 at 01:12 UTC
To check if something exists use exists. ;) `use strict; use warnings; require ('Encode.pm'); if (exists &Encode::encode) { print "Exists\n"; } else { print "None such\n"; }` [download] Prints: `Exists` [download] Perl reduces RSI - it saves typing	[reply] [d/l] [select]
Re^2: How to check if a function exists within a package? by ikegami (Patriarch) on Sep 08, 2008 at 01:29 UTC
`defined` vs `exists`: `sub foo {} sub bar; my @names = qw( foo bar baz ); local $, = "\t"; local $\ = "\n"; print('', @names); print('exists', map { exists(&$_) ?1:0 } @names); print('defined', map { defined(&$_) ?1:0 } @names);` [download] `foo bar baz exists 1 1 0 defined 1 0 0` [download] You can't call the ones that exist but aren't defined, so `defined` is probably a better choice. `>perl -e"sub bar; bar()" Undefined subroutine &main::bar called at -e line 1.` [download]	[reply] [d/l] [select]
Re: How to check if a function exists within a package? by codeacrobat (Chaplain) on Sep 08, 2008 at 18:55 UTC
I prefer a symbol table lookup. `perl -e ' package Foo; sub bar{42}; package main; print defined *Foo::bar{CODE}' 1` [download] This avoids ambiguity issues with using the ampersand. `print+qq(\L@{[ref\&@]}@{['@'x7^'!#2/"!4']});`	[reply] [d/l] [select]
Re^2: How to check if a function exists within a package? by Anonymous Monk on Jan 22, 2009 at 18:16 UTC
why not: sub method_exists_in_obj($$) { my $obj = shift;#object as href my $method = shift;#method name to test for return 1 if (defined(&{(ref $obj)."::".$method})); return 0; }	[reply]