Re: What's wrong with this local() ?

local $var;
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is functionally equivalent to

my $saved_var = $var;
ON_SCOPE_EXIT { $var = $saved_var; }
$var = undef;
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except local can be used in the middle of an expression (where it returns its arg as a lvalue).

Perhaps you want

local $A::variable = $A::variable;
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Comment on Re: What's wrong with this local() ? Select or Download Code

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Re^2: What's wrong with this local() ? (*) by tye (Sage) on Jan 30, 2008 at 08:14 UTC
Actually, it is closer to: `# Save a reference to the original variable: nothingToSeeHere::var= \$var; # Replace the variable with a new variable instance and assign # that new instance the given value (or undef if none mentioned): var= \undef; # (but see footnote) # Restore the previous instance (and thus the previous value): ON_SCOPE_EXIT { var= \$nothingToSeeHere::var; }` [download] That is, it is not just the value that is saved, but the scalar that holds that value. This can matter if the variable was tied or has other "magic" attached to it. It also matters if you have taken a reference to the original instance of the variable or take a reference to the new instance (they will point to different variables). It also means that the string value is not copied, as would happen with `$saved= $var;`. - tye ^ Actually, this step is less like `var= \undef;` (which leaves $var read-only) and perhaps more like `var= do { my $t= undef; \$t };`. But testing shows that the latter leaves $var marked "PADBUSY" and "PADMY" so it is perhaps even more like `*var= \[undef]->[0];`. Go figure. :)	[reply] [d/l] [select]

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Re^2: What's wrong with this local() ? (*)
by tye (Sage) on Jan 30, 2008 at 08:14 UTC

Actually, it is closer to:

# Save a reference to the original variable:
*nothingToSeeHere::var= \$var;
# Replace the variable with a new variable instance and assign
# that new instance the given value (or undef if none mentioned):
*var= \undef; # (but see footnote)
# Restore the previous instance (and thus the previous value):
ON_SCOPE_EXIT { *var= \$nothingToSeeHere::var; }
[download]

That is, it is not just the value that is saved, but the scalar that holds that value. This can matter if the variable was tied or has other "magic" attached to it. It also matters if you have taken a reference to the original instance of the variable or take a reference to the new instance (they will point to different variables). It also means that the string value is not copied, as would happen with $saved= $var;.

- tye

^* Actually, this step is less like *var= \undef; (which leaves $var read-only) and perhaps more like *var= do { my $t= undef; \$t };. But testing shows that the latter leaves $var marked "PADBUSY" and "PADMY" so it is perhaps even more like *var= \[undef]->[0];. Go figure. :)

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