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use warnings; 
use strict;

sub a       { "unchanged" };
sub print_a { print a(), "\n" };

no strict 'refs';
no warnings 'redefine';
...
    local *a = sub { "changed" };
    print_a();  # prints "changed"
}

print_a();      # prints "unchanged"

sub localize_a_and_call_fn(&@) {
    my ($fn, @args) = @_;
    local *a = sub { "changed" };
    $fn->(@args);
}

localize_a_and_call_fn( \&print_a );
# prints "changed"
...
    print "a() => ", a(), "\n";
};
# prints "a() => changed"

sub localize_and_call_fn
{
...
    local *$_ = sub { "changed" } for @$locals;
    $fn->(@args);
}

localize_and_call_fn( [qw(a b c)], \&print_a );
# prints "unchanged"

#     for (@$locals) {
#         local *$_ = sub { "changed" };
#     }

sub localize_and_call_fn_2
{
...

localize_and_call_fn_2( [qw(a b c)], \&print_a );
# prints "changed"

# (sub {
#     local *c = sub { "changed" };
...
#         })->(@_)
#     })->(@_)
# })->();