When expensive_call can return zero for a valid value or return undef to indicate failure, use the

D'Orcish Maneuver 

my @sorted = sort {
    ( $times{$a} //= expensive_call($a) ) <=>
    ( $times{$b} //= expensive_call($b) )
} @old_array;

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defined-or cache, needs defined-or (dor) operator introduced in 5.10

See also Resorting to Sorting, Sorting problem with Orcish Manuever

In reply to D'Orcish Maneuver by Anonymous Monk

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