#!/usr/bin/perl

use strict;
use warnings;


my $time = time;
sub f { localtime $time }
my %h = ( scalar f() => 1 );
print grep { defined } @h{+f} ? "not this" : "this prints", "\n";
print grep { defined } $h{+f} ? "this prints" : "not this", "\n";

Scalar value @h{+f} better written as $h{+f} at t.pl line 10.
this prints
this prints