Does my $_; do anything if $_ is implied - perl

Question

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 haven't used my $_; and I suspect it's a bug since I'm using it in a case where it's implied.

Answer 1

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
simple
my $_;
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 previously my'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;