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FAQ 7.19 What's the difference between deep and shallow binding?

 
 
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      04-13-2011
This is an excerpt from the latest version perlfaq7.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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7.19: What's the difference between deep and shallow binding?

In deep binding, lexical variables mentioned in anonymous subroutines
are the same ones that were in scope when the subroutine was created. In
shallow binding, they are whichever variables with the same names happen
to be in scope when the subroutine is called. Perl always uses deep
binding of lexical variables (i.e., those created with my()). However,
dynamic variables (aka global, local, or package variables) are
effectively shallowly bound. Consider this just one more reason not to
use them. See the answer to "What's a closure?".



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are not necessarily experts in every domain where Perl might show up,
so please include as much information as possible and relevant in any
corrections. The perlfaq-workers also don't have access to every
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Working code is greatly appreciated.

If you'd like to help maintain the perlfaq, see the details in
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