But it brings up another question. It implies that local can restore this binding. But Abigail's code on another thread implies that FETCH/STORE is used when localizing a tied variable, as opposed to just changing the binding. Does local work differently on tied variables, or is something else going on?

—John

Look carefully at the sequence and line numbers of the carp output from this:

use strict; use vars qw($obj); use Carp qw(carp croak cluck confess); use Cwd; sub TIESCALAR { my $var; carp "tie:\t",\$var," = $_[0]\n"; bless \$var + => shift; } sub FETCH { carp "fetch:\t$_[0] == ${$_[0]}\n"; ${$_[0]} } sub STORE { carp "store:\t$_[0] = $_[1]\n"; ${$_[0]} = $_[1]} tie $obj => 'main'; $obj = 'foo'; { my $x = 1; my $y = $obj; local $obj = 'bar'; } ### OUTPUT ### tie: SCALAR(0x8106d78) = main main::TIESCALAR('main') called at - line 10 store: main=SCALAR(0x8106d78) = foo main::STORE('main=SCALAR(0x8106d78)', 'foo') called at - line +11 fetch: main=SCALAR(0x8106d78) == foo main::FETCH('main=SCALAR(0x8106d78)') called at - line 14 fetch: main=SCALAR(0x8106d78) == foo main::FETCH('main=SCALAR(0x8106d78)') called at - line 15 store: main=SCALAR(0x8106d78) = main::STORE('main=SCALAR(0x8106d78)', undef) called at - line +15 store: main=SCALAR(0x8106d78) = bar main::STORE('main=SCALAR(0x8106d78)', 'bar') called at - line +15 store: main=SCALAR(0x8106d78) = foo main::STORE('main=SCALAR(0x8106d78)', 'foo') called at - line +13 [download]

I'm not sure exactly what you're asking, but I think this may answer your question :-)

   MeowChow                                   
               s aamecha.s a..a\u$&owag.print

Yes, that matches what this node relies on, that local works by saving the old value and restoring it, exactly like assignments would. In your example, $obj is always pointing to the same SV.

However, using Alias, e.g. from the module:

@DYNAMIC = qw(m n o);
{
 local @DYNAMIC;
 alias DYNAMIC => $tmp, PERM => $tmp;
 $DYNAMIC[2] = 'zzz';
 # prints "abzzzd|abzzzd|abzzzd"
 print @$tmp, "|", @DYNAMIC, "|", @PERM, "\n";
 }
# prints "mno|pqr"
print @DYNAMIC, "|", @PERM, "\n";
[download]

The Alias re-binds the symbol @DYNAMIC, essentially the same as *DYNAMIC=$tmp;. @DYNAMIC now aliases @$tmp.

But look at the local. It will restore the list @DYNAMIC, which means it will un-do this binding operation. If going out of scope does a STORE as you show, essentially @DYNAMIC=@saved;, it will overwrite the contents of @$tmp, as opposed to restoring the action of the *DYNAMIC=$tmp;. Follow me? He did not say local *DYNAMIC.

If local worked by pointing the symbol to a new SV, then there would be no need to FETCH/STORE, and the tie would not be preserved.

So there is still more to it than meets the eye.

—John