alamb edited a comment on pull request #1437:
URL: https://github.com/apache/arrow-datafusion/pull/1437#issuecomment-992770032
> > This is an acceptable short term workaround, but I think it would be
more efficient and more elegant if we rewrite these recursive procedures into
iterative procedures.
> Do you mean to use push-based model？
@xudong963 , I think what @houqp is suggesting is to rewrite code that is
recursive to not be recursive.
The pattern for Datafusion probably looks like taking code like
```rust
fn visit(expr: &expr) {
for child in expr.children() {
visit(child)
}
// do actual expr logic
}
```
And changing it so the state is tracked with a structure on the heap rather
than a stack. I think
[`VecDeque`](https://doc.rust-lang.org/stable/std/collections/struct.VecDeque.html)
is a good one for rust:
```rust
fn visit(expr: &expr) {
let mut worklist = VecDequeue::new();
worklist.push_back(expr);
while !worklist.is_empty() {
let parent = worklist.pop_front();
for child in parent.children() {
worklist.push_back(child)
}
// do actual expr logic on parent
}
}
```
(aka avoid the call back to `visit`)
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