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use crate::docset::DocSet;

/// Postings (also called inverted list)
///
/// For a given term, it is the list of doc ids of the doc
/// containing the term. Optionally, for each document,
/// it may also give access to the term frequency
/// as well as the list of term positions.
///
/// Its main implementation is `SegmentPostings`,
/// but other implementations mocking `SegmentPostings` exist,
/// for merging segments or for testing.
pub trait Postings: DocSet + 'static {
    /// Returns the term frequency
    fn term_freq(&self) -> u32;

    /// Returns the positions offseted with a given value.
    /// The output vector will be resized to the `term_freq`.
    fn positions_with_offset(&mut self, offset: u32, output: &mut Vec<u32>);

    /// Returns the positions of the term in the given document.
    /// The output vector will be resized to the `term_freq`.
    fn positions(&mut self, output: &mut Vec<u32>) {
        self.positions_with_offset(0u32, output);
    }
}