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use DocId;
use std::borrow::Borrow;
use std::borrow::BorrowMut;
use std::cmp::Ordering;
/// Expresses the outcome of a call to `DocSet`'s `.skip_next(...)`.
#[derive(PartialEq, Eq, Debug)]
pub enum SkipResult {
/// target was in the docset
Reached,
/// target was not in the docset, skipping stopped as a greater element was found
OverStep,
/// the docset was entirely consumed without finding the target, nor any
/// element greater than the target.
End,
}
/// Represents an iterable set of sorted doc ids.
pub trait DocSet {
/// Goes to the next element.
/// `.advance(...)` needs to be called a first time to point to the correct
/// element.
fn advance(&mut self) -> bool;
/// After skipping, position the iterator in such a way that `.doc()`
/// will return a value greater than or equal to target.
///
/// SkipResult expresses whether the `target value` was reached, overstepped,
/// or if the `DocSet` was entirely consumed without finding any value
/// greater or equal to the `target`.
///
/// WARNING: Calling skip always advances the docset.
/// More specifically, if the docset is already positionned on the target
/// skipping will advance to the next position and return SkipResult::Overstep.
///
fn skip_next(&mut self, target: DocId) -> SkipResult {
if !self.advance() {
return SkipResult::End;
}
loop {
match self.doc().cmp(&target) {
Ordering::Less => {
if !self.advance() {
return SkipResult::End;
}
}
Ordering::Equal => return SkipResult::Reached,
Ordering::Greater => return SkipResult::OverStep,
}
}
}
/// Returns the current document
fn doc(&self) -> DocId;
/// Advances the cursor to the next document
/// None is returned if the iterator has `DocSet`
/// has already been entirely consumed.
fn next(&mut self) -> Option<DocId> {
if self.advance() {
Some(self.doc())
} else {
None
}
}
/// Returns a best-effort hint of the
/// length of the docset.
fn size_hint(&self) -> usize;
}
impl<TDocSet: DocSet + ?Sized> DocSet for Box<TDocSet> {
fn advance(&mut self) -> bool {
let unboxed: &mut TDocSet = self.borrow_mut();
unboxed.advance()
}
fn skip_next(&mut self, target: DocId) -> SkipResult {
let unboxed: &mut TDocSet = self.borrow_mut();
unboxed.skip_next(target)
}
fn doc(&self) -> DocId {
let unboxed: &TDocSet = self.borrow();
unboxed.doc()
}
fn size_hint(&self) -> usize {
let unboxed: &TDocSet = self.borrow();
unboxed.size_hint()
}
}
impl<'a, TDocSet: DocSet> DocSet for &'a mut TDocSet {
fn advance(&mut self) -> bool {
let unref: &mut TDocSet = *self;
unref.advance()
}
fn skip_next(&mut self, target: DocId) -> SkipResult {
let unref: &mut TDocSet = *self;
unref.skip_next(target)
}
fn doc(&self) -> DocId {
let unref: &TDocSet = *self;
unref.doc()
}
fn size_hint(&self) -> usize {
let unref: &TDocSet = *self;
unref.size_hint()
}
}
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