presto-main/src/main/java/io/prestosql/sql/gen/ExpressionCompiler.java/ExpressionCompiler/CacheKey
class ExpressionCompiler:        private CacheKey(Optional<RowExpression> filter, List<? extends RowExpression> projections, Object uniqueKey)
        {
            this.filter = filter;
            this.uniqueKey = uniqueKey;
            this.projections = ImmutableList.copyOf(projections);
        }