datafusion/common/src/alias.rs

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// to you under the Apache License, Version 2.0 (the
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//
//   http://www.apache.org/licenses/LICENSE-2.0
//
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use std::sync::atomic::{AtomicUsize, Ordering};

/// A utility struct that can be used to generate unique aliases when optimizing queries
#[derive(Debug)]
pub struct AliasGenerator {
    next_id: AtomicUsize,
}

impl Default for AliasGenerator {
    fn default() -> Self {
        Self {
            next_id: AtomicUsize::new(1),
        }
    }
}

impl AliasGenerator {
    /// Create a new [`AliasGenerator`]
    pub fn new() -> Self {
        Self::default()
    }

    /// Advance the counter to at least `min_id`, ensuring future aliases
    /// won't collide with already-existing ones.
    ///
    /// For example, if the query already contains an alias `alias_42`, then calling
    /// `update_min_id(42)` will ensure that future aliases generated by this
    /// [`AliasGenerator`] will start from `alias_43`.
    pub fn update_min_id(&self, min_id: usize) {
        self.next_id.fetch_max(min_id + 1, Ordering::Relaxed);
    }

    /// Return a unique alias with the provided prefix
    pub fn next(&self, prefix: &str) -> String {
        let id = self.next_id.fetch_add(1, Ordering::Relaxed);
        format!("{prefix}_{id}")
    }
}