Currently class SqlNodeList [1] implements Iterable<SqlNode> but it does not implement List<SqlNode>. How do people feel about doing that? (Or Collection<SqlNode>?)
The main potential benefit is performance. Consider this code: SqlNodeList nodeList; ImmutableList immutableList1 = ImmutableList.copyOf(nodeList); List<SqlNode> list = nodeList.toList(); ImmutableList immutableList2 = ImmutableList.copyOf(list); Today, the second form is faster, because ImmutableList.copyOf can call size() and preallocate a list of the right size. The second benefit is that we can remove calls to '.toList()'. The downside is that a few locations are overloaded. For example, class Span has overloaded methods static Span of(SqlNode node); static Span of(Collection<? extends SqlNode> nodes) If SqlNodeList implements List<? extends SqlNode>, then the code SqlNodeList nodeList; Span s = Span.of(nodeList); becomes ambiguous. We can disambiguate by adding Span.of(SqlNodeList). But there may be other locations in client code that cannot be disambiguated. Julian [1] https://github.com/apache/calcite/blob/155276591288615c4d02d55fb7d77eceb2e24b2d/core/src/main/java/org/apache/calcite/sql/SqlNodeList.java#L38
