my $bar = expensive();
$foo = $bar if defined $bar;

##</code><code>##

if (defined(my $bar = expensive())) {
   $foo = $bar;
}

##</code><code>##

$foo = $_ for grep defined, expensive();

##</code><code>##

sub assign_ifdef { $_[0] = $_[1] if defined($_[1]) }

assign_ifdef($foo, expensive());

##</code><code>##

my $bar = expensive();
($i1, $i2) = $bar if defined $bar;

##</code><code>##

if (defined(my $bar = expensive()) {
   $_ = $bar for $i1, $i2;
}