use With;

my $foo = "a string";

print "before with: $foo\n";
with($foo) {
  s/a /not a /;
}
print "after with:  $foo\n";

with(foo) {
  sub new {
    bless {}, shift;
  }
}

print foo->new;

__output__

before with: a string
after with:  not a string
foo=HASH(0x80fbbf0)