uqa-execution 0.4.6

Volcano physical operators with row-batch pipelines
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//
// Unified Query Algebra
//
// Copyright (c) 2023-2026 Cognica, Inc.
//

//! Borrowed value traversal keeps its explicit stack in the selected allowance.

use super::{output::resource_error, BudgetedVec, ExecResult, StorageReadControl, Value};

pub(super) enum Children<'a> {
    Values(std::slice::Iter<'a, Value>),
    Record(std::slice::Iter<'a, (String, Value)>),
    Map(std::collections::btree_map::Iter<'a, String, Value>),
}

impl<'a> Children<'a> {
    pub(super) fn next(&mut self) -> Option<(Option<&'a str>, &'a Value)> {
        match self {
            Self::Values(values) => values.next().map(|value| (None, value)),
            Self::Record(fields) => fields.next().map(|(_, value)| (None, value)),
            Self::Map(fields) => fields
                .next()
                .map(|(name, value)| (Some(name.as_str()), value)),
        }
    }
}

pub(super) enum Frames<'a> {
    Owned(Vec<Children<'a>>),
    Budgeted(BudgetedVec<Children<'a>>),
}

impl<'a> Frames<'a> {
    pub(super) fn new(control: Option<&StorageReadControl>) -> Self {
        match control {
            Some(control) => Self::Budgeted(BudgetedVec::new(control.memory())),
            None => Self::Owned(Vec::new()),
        }
    }

    pub(super) fn push(&mut self, value: Children<'a>) -> ExecResult<()> {
        match self {
            Self::Owned(values) => values.push(value),
            Self::Budgeted(values) => values.push(value).map_err(resource_error)?,
        }
        Ok(())
    }

    pub(super) fn last_mut(&mut self) -> Option<&mut Children<'a>> {
        match self {
            Self::Owned(values) => values.last_mut(),
            Self::Budgeted(values) => values.last_mut(),
        }
    }

    pub(super) fn pop(&mut self) {
        match self {
            Self::Owned(values) => {
                values.pop();
            }
            Self::Budgeted(values) => {
                values.pop();
            }
        }
    }
}