#!/usr/bin/perl

use v5.16;

use warnings;
use Benchmark qw/cmpthese/;

my $foo = {
    bar => 'baz',
    baz => undef,
};

my $foo1 = {};

sub _ifdefined {
    for ( keys(%{$foo}) ) {
        $foo1->{$_} = 'default' unless defined($foo->{$_});
    }
}

sub _definedor {
    for ( keys(%{$foo}) ) {
        $foo1->{$_} //= 'default';
    }
}

cmpthese(
    -5,
    {
        _ifdefined => sub { _ifdefined() },
        _definedor  => sub { _definedor() },
    }
);

exit;

__END__

Output:
                Rate _ifdefined _definedor
_ifdefined 1081314/s         --       -12%
_definedor 1228949/s        14%         --