presto-main/src/main/java/io/prestosql/sql/planner/optimizations/HashGenerationOptimizer.java/HashComputationSet/translate
class HashComputationSet:        public HashComputationSet translate(Function<Symbol, Optional<Symbol>> translator)
        {
            ImmutableSetMultimap.Builder<HashComputation, HashComputation> builder = ImmutableSetMultimap.builder();
            for (HashComputation hashComputation : hashes.keySet()) {
                hashComputation.translate(translator)
                        .ifPresent(hash -> builder.put(hash, hashComputation));
            }
            return new HashComputationSet(builder.build());
        }