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Re: Advanced subroutine and symbol table manipultation

by blokhead (Monsignor)
on Jul 16, 2004 at 21:13 UTC ( #375137=note: print w/ replies, xml ) Need Help??


in reply to Advanced subroutine and symbol table manipultation

Zaxo's answer is probably the best for just using a pre-call hook. But if you need a little more control over calling the old sub, you may need to do it yourself.

I don't see the problem with strict. Just turn off strict refs locally and use symbolic references, it's a lot easier than messing with eval. Part of strict is knowing when you should turn it off. Messing with the symbol table is one of those times. Just make sure you don't turn off strict refs inside that closure that becomes the new sub, though.

package Foo; sub bar { print "Original Foo::bar\n"; } package main; sub switcheroo { my ($pkg, $func) = @_; my $old_ref = do { no strict 'refs'; \&{"$pkg\::$func"}; }; my $new_ref = sub { print "New $func\n"; $old_ref->(); }; { no strict 'refs'; *{"$pkg\::$func"} = $new_ref; } } Foo::bar(); switcheroo("Foo", "bar"); Foo::bar();
You may also want to use goto &$old_ref in case the original sub wanted to look at caller.

blokhead


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Re^2: Advanced subroutine and symbol table manipultation
by Tuppence (Pilgrim) on Jul 16, 2004 at 22:47 UTC

    Wow, that's great too. I added a 'use strict' to the top of it and it still works great.

    I think I was getting confused because I was under the impression that you must undef the subroutine before you can redefine it, and I was having trouble getting undef $var to not undef $var itself but the function name stored in $var.

    Thanks!

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