knight makes a good point. Fortunately, in Perl 6, there will be a defaulting operator to simplify this very problem.

A binary // operator is the defaulting operator.
That is:

$a // $b
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is short for:

defined($a) ?? $a :: $b
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except that the left side is evaluated only once. It will work on arrays and hashes as well as scalars. It also has a corresponding assignment operator, which only does the assignment if the left side is undefined:

$pi //= 3;
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Perl 6 should be such fun!