polars-plan 0.54.3

Lazy query engine for the Polars DataFrame library
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//! Keys in the `acc_predicates` hashmap.
use super::*;

// an invisible ascii token we use as delimiter
const HIDDEN_DELIMITER: &str = "\u{1D17A}";

/// Determine the hashmap key by combining all the leaf column names of a predicate
pub(super) fn predicate_to_key(predicate: Node, expr_arena: &Arena<AExpr>) -> PlSmallStr {
    let mut iter = aexpr_to_leaf_names_iter(predicate, expr_arena);
    if let Some(first) = iter.next() {
        if let Some(second) = iter.next() {
            let mut new = String::with_capacity(32 * iter.size_hint().0);
            new.push_str(first);
            new.push_str(HIDDEN_DELIMITER);
            new.push_str(second);

            for name in iter {
                new.push_str(HIDDEN_DELIMITER);
                new.push_str(name);
            }
            return PlSmallStr::from_string(new);
        }
        first.clone()
    } else {
        PlSmallStr::from_str(HIDDEN_DELIMITER)
    }
}