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One problem with using dynamic scoping is that you've opened up the possibility that the same variable could be used somewhere else for a different purpose. That is the advantage to using lexicals.

Another solution is to use ReleaseAction to do cleanup when you exit the sub.

sub outer { my $helper; $helper = sub { ... }; my $delay_cleanup = on_release {$helper = undef}; $helper->(@_); }
Effectively it does the same thing as the weaken solution, but the code is a little more explicit about what is happening, when. I'd personally lean towards this solution.

And a final option. Larry thinks that using dynamic scoping on lexical variables is too confusing to allow. But he does allow it for data structures. Which leads to the convoluted:

sub outer { my @helper; local $helper[0] = sub { ... }; $helper[0]->(@_); }
I wouldn't suggest this solution for fear of the psychopathic maintenance programmer demanding to know why this works. But every year or two I wind up using this fact in a recursive function to detect and track down potential deep recursion bugs. For instance I'm recursing through a set of nodes and I'll do something like this:
{ my %in_node; sub something_recursive { my $node = shift; if ($in_node{$node->{name}}) { confess("Can't access $node->{name} while accessing $node->{name +}"); } local $in_node{$node->{name}} = 1; ... } }

In reply to Re: Creating Nested Functions by tilly
in thread Creating Nested Functions by ikegami

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