alamb commented on issue #1972:
URL:
https://github.com/apache/arrow-datafusion/issues/1972#issuecomment-1064152946
I was imagining an actual mutator like this:
```rust
trait LogicalPlanRewriter {
pub fn rewrite(plan: LogicalPlan) -> Result<LogicalPlan>
}
```
that would handle the traversal into children so that each optimizer would
look something like
```rust
impl LogicalPlanRewriter for MyOptimizerPass {
fn rewrite(plan: LogicalPlan) -> Result<LogicalPlan> {
match plan {
// special handling for the types of plans the optimizer cares about
LogicalPlan::Filter(..) => {...}
...
// default is no rewrite
_ => Ok(plan)
}
}
```
I vaguely remember trying to write something like this up once, but as I
recall I got stuck on the fact that `LogicalPlans` can have shared inputs
(there are `Arcs` ?) but I can't remember exactly and it was a while ago.
A slight variant on the above that looks more like a typical vistitor would
be something that handled each type of LogicalPlan and defaults to itself and
could save the switch statement:
```rust
trait LogicalPlanRewriter {
// rewrite a LogicalPlan filter node; Default implementation returns the
same plan
pub fn rewrite_filter(filter: Filter) -> Result<LogicalPlan> {
Ok(LogicalPlan::Filter(filter)
}
// rewrite a LogicalPlan table_scan node; Default implementation returns
the same plan
pub fn rewrite_filter(table_scan: TableScan) -> Result<LogicalPlan> {
Ok(LogicalPlan::TableScan(table_scan)
}
...
}
```
What do you think?
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