Does my $_; do anything if $_ is implied
I think the answer is yes but I just want to make sure. so if I have
sub something {
my $_;
my @array = ...;
while ( @array ) {
say;
}
}
is the my $_;
actually effective at lexicalizing the parameter passed to the say?
In this particular case I'm using the DZP::UnusedVarsTests and it's complaining that I ha开发者_Python百科ven't used my $_;
and I suspect it's a bug since I'm using it in a case where it's implied.
The short answer is Yes. It makes the functions in that scope use the lexically scoped $_
, and not the global $_
. If they write back to $_
, as in the case of s///
, you will have some level of damage control.
Per perldoc perldelta
(5.10.0):
"
List::Util::first
" misbehaves in the presence of a lexical$_
(typically introduced by "my $_
" or implicitly by "given
"). The variable which gets set for each iteration is the package variable$_
, not the lexical$_
[RT #67694].A similar issue may occur in other modules that provide functions which take a block as their first argument, like
foo { ... $_ ...} list
And, in perldoc perl591delta
it goes on to say:
Lexical $_
The default variable
$_
can now be lexicalized, by declaring it like any other lexical variable, with a simplemy $_;
The operations that default on
$_
will use the lexically-scoped version of$_
when it exists, instead of the global$_
.In a "
map
" or a "grep
" block, if$_
was previouslymy
'ed, then the$_
inside the block is lexical as well (and scoped to the block).In a scope where
$_
has been lexicalized, you can still have access to the global version of$_
by using$::_
, or, more simply, by overriding the lexical declaration with "our $_
".
Examples
I wanted to provide some examples of why this functionality would be used:
my $_ = 'BOOM!';
sub something {
my $_; ## Try running with and without
my @array = qw/foo bar baz/;
while ( $_ = pop @array ) {
say;
}
}
something();
say;
And, another example
my $_ = 'foo';
sub something {
my $_ = $_; ## Try running with and without
s/foo/bar/;
$_;
}
something();
say;
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