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use std::fmt; use std::iter::FromIterator; use std::io; use std::path::Path; use automaton::{Automaton, AlwaysMatch}; use raw; use stream::{IntoStreamer, Streamer}; use Result; /// Set is a lexicographically ordered set of byte strings. /// /// A `Set` is constructed with the `SetBuilder` type. Alternatively, a `Set` /// can be constructed in memory from a lexicographically ordered iterator /// of byte strings (`Set::from_iter`). /// /// A key feature of `Set` is that it can be serialized to disk compactly. Its /// underlying representation is built such that the `Set` can be memory mapped /// (`Set::from_path`) and searched without necessarily loading the entire /// set into memory. /// /// It supports most common operations associated with sets, such as /// membership, union, intersection, subset/superset, etc. It also supports /// range queries and automata based searches (e.g. a regular expression). /// /// Sets are represented by a finite state transducer where output values are /// always zero. As such, sets have the following invariants: /// /// 1. Once constructed, a `Set` can never be modified. /// 2. Sets must be constructed with lexicographically ordered byte sequences. pub struct Set(raw::Fst); impl Set { /// Opens a set stored at the given file path via a memory map. /// /// The set must have been written with a compatible finite state /// transducer builder (`SetBuilder` qualifies). If the format is invalid /// or if there is a mismatch between the API version of this library /// and the set, then an error is returned. pub fn from_path<P: AsRef<Path>>(path: P) -> Result<Self> { raw::Fst::from_path(path).map(Set) } /// Creates a set from its representation as a raw byte sequence. /// /// Note that this operation is very cheap (no allocations and no copies). /// /// The set must have been written with a compatible finite state /// transducer builder (`SetBuilder` qualifies). If the format is invalid /// or if there is a mismatch between the API version of this library /// and the set, then an error is returned. pub fn from_bytes(bytes: Vec<u8>) -> Result<Self> { raw::Fst::from_bytes(bytes).map(Set) } /// Create a `Set` from an iterator of lexicographically ordered byte /// strings. /// /// If the iterator does not yield values in lexicographic order, then an /// error is returned. /// /// Note that this is a convenience function to build a set in memory. /// To build a set that streams to an arbitrary `io::Write`, use /// `SetBuilder`. pub fn from_iter<T, I>(iter: I) -> Result<Self> where T: AsRef<[u8]>, I: IntoIterator<Item=T> { let mut builder = SetBuilder::memory(); try!(builder.extend_iter(iter)); Set::from_bytes(try!(builder.into_inner())) } /// Tests the membership of a single key. /// /// # Example /// /// ```rust /// use fst::Set; /// /// let set = Set::from_iter(&["a", "b", "c"]).unwrap(); /// /// assert_eq!(set.contains("b"), true); /// assert_eq!(set.contains("z"), false); /// ``` pub fn contains<K: AsRef<[u8]>>(&self, key: K) -> bool { self.0.contains_key(key) } /// Return a lexicographically ordered stream of all keys in this set. /// /// While this is a stream, it does require heap space proportional to the /// longest key in the set. /// /// If the set is memory mapped, then no further heap space is needed. /// Note though that your operating system may fill your page cache /// (which will cause the resident memory usage of the process to go up /// correspondingly). /// /// # Example /// /// Since streams are not iterators, the traditional `for` loop cannot be /// used. `while let` is useful instead: /// /// ```rust /// use fst::{IntoStreamer, Streamer, Set}; /// /// let set = Set::from_iter(&["a", "b", "c"]).unwrap(); /// let mut stream = set.stream(); /// /// let mut keys = vec![]; /// while let Some(key) = stream.next() { /// keys.push(key.to_vec()); /// } /// assert_eq!(keys, vec![b"a", b"b", b"c"]); /// ``` pub fn stream(&self) -> Stream { Stream(self.0.stream()) } /// Return a builder for range queries. /// /// A range query returns a subset of keys in this set in a range given in /// lexicographic order. /// /// Memory requirements are the same as described on `Set::stream`. /// Notably, only the keys in the range are read; keys outside the range /// are not. /// /// # Example /// /// Returns only the keys in the range given. /// /// ```rust /// use fst::{IntoStreamer, Streamer, Set}; /// /// let set = Set::from_iter(&["a", "b", "c", "d", "e"]).unwrap(); /// let mut stream = set.range().ge("b").lt("e").into_stream(); /// /// let mut keys = vec![]; /// while let Some(key) = stream.next() { /// keys.push(key.to_vec()); /// } /// assert_eq!(keys, vec![b"b", b"c", b"d"]); /// ``` pub fn range(&self) -> StreamBuilder { StreamBuilder(self.0.range()) } /// Executes an automaton on the keys of this set. /// /// Note that this returns a `StreamBuilder`, which can be used to /// add a range query to the search (see the `range` method). /// /// Memory requirements are the same as described on `Set::stream`. /// /// # Example /// /// This crate provides an implementation of regular expressions /// for `Automaton`. Make sure to see the documentation for `fst::Regex` /// for more details such as what kind of regular expressions are allowed. /// /// ```rust /// use fst::{IntoStreamer, Streamer, Regex, Set}; /// /// let set = Set::from_iter(&["foo", "foo1", "foo2", "foo3", "foobar"]) /// .unwrap(); /// /// let re = Regex::new("f[a-z]+3?").unwrap(); /// let mut stream = set.search(&re).into_stream(); /// /// let mut keys = vec![]; /// while let Some(key) = stream.next() { /// keys.push(key.to_vec()); /// } /// assert_eq!(keys, vec![ /// "foo".as_bytes(), "foo3".as_bytes(), "foobar".as_bytes(), /// ]); /// ``` pub fn search<A: Automaton>(&self, aut: A) -> StreamBuilder<A> { StreamBuilder(self.0.search(aut)) } /// Returns the number of elements in this set. pub fn len(&self) -> usize { self.0.len() } /// Returns true if and only if this set is empty. pub fn is_empty(&self) -> bool { self.0.is_empty() } /// Creates a new set operation with this set added to it. /// /// The `OpBuilder` type can be used to add additional set streams /// and perform set operations like union, intersection, difference and /// symmetric difference. /// /// # Example /// /// ```rust /// use fst::{IntoStreamer, Streamer, Set}; /// /// let set1 = Set::from_iter(&["a", "b", "c"]).unwrap(); /// let set2 = Set::from_iter(&["a", "y", "z"]).unwrap(); /// /// let mut union = set1.op().add(&set2).union(); /// /// let mut keys = vec![]; /// while let Some(key) = union.next() { /// keys.push(key.to_vec()); /// } /// assert_eq!(keys, vec![b"a", b"b", b"c", b"y", b"z"]); /// ``` pub fn op(&self) -> OpBuilder { OpBuilder::new().add(self) } /// Returns true if and only if the `self` set is disjoint with the set /// `stream`. /// /// `stream` must be a lexicographically ordered sequence of byte strings. /// /// # Example /// /// ```rust /// use fst::{IntoStreamer, Streamer, Set}; /// /// let set1 = Set::from_iter(&["a", "b", "c"]).unwrap(); /// let set2 = Set::from_iter(&["x", "y", "z"]).unwrap(); /// /// assert_eq!(set1.is_disjoint(&set2), true); /// /// let set3 = Set::from_iter(&["a", "c"]).unwrap(); /// /// assert_eq!(set1.is_disjoint(&set3), false); /// ``` pub fn is_disjoint<'f, I, S>(&self, stream: I) -> bool where I: for<'a> IntoStreamer<'a, Into=S, Item=&'a [u8]>, S: 'f + for<'a> Streamer<'a, Item=&'a [u8]> { self.0.is_disjoint(StreamZeroOutput(stream.into_stream())) } /// Returns true if and only if the `self` set is a subset of `stream`. /// /// `stream` must be a lexicographically ordered sequence of byte strings. /// /// # Example /// /// ```rust /// use fst::Set; /// /// let set1 = Set::from_iter(&["a", "b", "c"]).unwrap(); /// let set2 = Set::from_iter(&["x", "y", "z"]).unwrap(); /// /// assert_eq!(set1.is_subset(&set2), false); /// /// let set3 = Set::from_iter(&["a", "c"]).unwrap(); /// /// assert_eq!(set1.is_subset(&set3), false); /// assert_eq!(set3.is_subset(&set1), true); /// ``` pub fn is_subset<'f, I, S>(&self, stream: I) -> bool where I: for<'a> IntoStreamer<'a, Into=S, Item=&'a [u8]>, S: 'f + for<'a> Streamer<'a, Item=&'a [u8]> { self.0.is_subset(StreamZeroOutput(stream.into_stream())) } /// Returns true if and only if the `self` set is a superset of `stream`. /// /// `stream` must be a lexicographically ordered sequence of byte strings. /// /// # Example /// /// ```rust /// use fst::Set; /// /// let set1 = Set::from_iter(&["a", "b", "c"]).unwrap(); /// let set2 = Set::from_iter(&["x", "y", "z"]).unwrap(); /// /// assert_eq!(set1.is_superset(&set2), false); /// /// let set3 = Set::from_iter(&["a", "c"]).unwrap(); /// /// assert_eq!(set1.is_superset(&set3), true); /// assert_eq!(set3.is_superset(&set1), false); /// ``` pub fn is_superset<'f, I, S>(&self, stream: I) -> bool where I: for<'a> IntoStreamer<'a, Into=S, Item=&'a [u8]>, S: 'f + for<'a> Streamer<'a, Item=&'a [u8]> { self.0.is_superset(StreamZeroOutput(stream.into_stream())) } /// Returns a reference to the underlying raw finite state transducer. pub fn as_fst(&self) -> &raw::Fst { &self.0 } } impl fmt::Debug for Set { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { try!(write!(f, "Set([")); let mut stream = self.stream(); let mut first = true; while let Some(key) = stream.next() { if !first { try!(write!(f, ", ")); } first = false; try!(write!(f, "{}", String::from_utf8_lossy(key))); } write!(f, "])") } } /// Returns the underlying finite state transducer. impl AsRef<raw::Fst> for Set { fn as_ref(&self) -> &raw::Fst { &self.0 } } impl<'s, 'a> IntoStreamer<'a> for &'s Set { type Item = &'a [u8]; type Into = Stream<'s>; fn into_stream(self) -> Self::Into { Stream(self.0.stream()) } } // Construct a set from an Fst object. impl From<raw::Fst> for Set { fn from(fst: raw::Fst) -> Set { Set(fst) } } /// A builder for creating a set. /// /// This is not your average everyday builder. It has two important qualities /// that make it a bit unique from what you might expect: /// /// 1. All keys must be added in lexicographic order. Adding a key out of order /// will result in an error. /// 2. The representation of a set is streamed to *any* `io::Write` as it is /// built. For an in memory representation, this can be a `Vec<u8>`. /// /// Point (2) is especially important because it means that a set can be /// constructed *without storing the entire set in memory*. Namely, since it /// works with any `io::Write`, it can be streamed directly to a file. /// /// With that said, the builder does use memory, but **memory usage is bounded /// to a constant size**. The amount of memory used trades off with the /// compression ratio. Currently, the implementation hard codes this trade off /// which can result in about 5-20MB of heap usage during construction. (N.B. /// Guaranteeing a maximal compression ratio requires memory proportional to /// the size of the set, which defeats the benefit of streaming it to disk. /// In practice, a small bounded amount of memory achieves close-to-minimal /// compression ratios.) /// /// The algorithmic complexity of set construction is `O(n)` where `n` is the /// number of elements added to the set. /// /// # Example: build in memory /// /// This shows how to use the builder to construct a set in memory. Note that /// `Set::from_iter` provides a convenience function that achieves this same /// goal without needing to explicitly use `SetBuilder`. /// /// ```rust /// use fst::{IntoStreamer, Streamer, Set, SetBuilder}; /// /// let mut build = SetBuilder::memory(); /// build.insert("bruce").unwrap(); /// build.insert("clarence").unwrap(); /// build.insert("stevie").unwrap(); /// /// // You could also call `finish()` here, but since we're building the set in /// // memory, there would be no way to get the `Vec<u8>` back. /// let bytes = build.into_inner().unwrap(); /// /// // At this point, the set has been constructed, but here's how to read it. /// let set = Set::from_bytes(bytes).unwrap(); /// let mut stream = set.into_stream(); /// let mut keys = vec![]; /// while let Some(key) = stream.next() { /// keys.push(key.to_vec()); /// } /// assert_eq!(keys, vec![ /// "bruce".as_bytes(), "clarence".as_bytes(), "stevie".as_bytes(), /// ]); /// ``` /// /// # Example: stream to file /// /// This shows how to stream construction of a set to a file. /// /// ```rust,no_run /// use std::fs::File; /// use std::io; /// /// use fst::{IntoStreamer, Streamer, Set, SetBuilder}; /// /// let mut wtr = io::BufWriter::new(File::create("set.fst").unwrap()); /// let mut build = SetBuilder::new(wtr).unwrap(); /// build.insert("bruce").unwrap(); /// build.insert("clarence").unwrap(); /// build.insert("stevie").unwrap(); /// /// // If you want the writer back, then call `into_inner`. Otherwise, this /// // will finish construction and call `flush`. /// build.finish().unwrap(); /// /// // At this point, the set has been constructed, but here's how to read it. /// let set = Set::from_path("set.fst").unwrap(); /// let mut stream = set.into_stream(); /// let mut keys = vec![]; /// while let Some(key) = stream.next() { /// keys.push(key.to_vec()); /// } /// assert_eq!(keys, vec![ /// "bruce".as_bytes(), "clarence".as_bytes(), "stevie".as_bytes(), /// ]); /// ``` pub struct SetBuilder<W>(raw::Builder<W>); impl SetBuilder<Vec<u8>> { /// Create a builder that builds a set in memory. pub fn memory() -> Self { SetBuilder(raw::Builder::memory()) } } impl<W: io::Write> SetBuilder<W> { /// Create a builder that builds a set by writing it to `wtr` in a /// streaming fashion. pub fn new(wtr: W) -> Result<SetBuilder<W>> { raw::Builder::new_type(wtr, 0).map(SetBuilder) } /// Insert a new key into the set. /// /// If a key is inserted that is less than any previous key added, then /// an error is returned. Similarly, if there was a problem writing to /// the underlying writer, an error is returned. pub fn insert<K: AsRef<[u8]>>(&mut self, key: K) -> Result<()> { self.0.add(key) } /// Calls insert on each item in the iterator. /// /// If an error occurred while adding an element, processing is stopped /// and the error is returned. pub fn extend_iter<T, I>(&mut self, iter: I) -> Result<()> where T: AsRef<[u8]>, I: IntoIterator<Item=T> { self.0.extend_iter(iter.into_iter() .map(|key| (key, raw::Output::zero()))) } /// Calls insert on each item in the stream. /// /// Note that unlike `extend_iter`, this is not generic on the items in /// the stream. pub fn extend_stream<'f, I, S>(&mut self, stream: I) -> Result<()> where I: for<'a> IntoStreamer<'a, Into=S, Item=&'a [u8]>, S: 'f + for<'a> Streamer<'a, Item=&'a [u8]> { self.0.extend_stream(StreamZeroOutput(stream.into_stream())) } /// Finishes the construction of the set and flushes the underlying /// writer. After completion, the data written to `W` may be read using /// one of `Set`'s constructor methods. pub fn finish(self) -> Result<()> { self.0.finish() } /// Just like `finish`, except it returns the underlying writer after /// flushing it. pub fn into_inner(self) -> Result<W> { self.0.into_inner() } } /// A lexicographically ordered stream of keys from a set. /// /// The `A` type parameter corresponds to an optional automaton to filter /// the stream. By default, no filtering is done. /// /// The `'s` lifetime parameter refers to the lifetime of the underlying set. pub struct Stream<'s, A=AlwaysMatch>(raw::Stream<'s, A>) where A: Automaton; impl<'s, A: Automaton> Stream<'s, A> { /// Creates a new set stream from an fst stream. /// /// Not part of the public API, but useful in sibling module `map`. #[doc(hidden)] pub fn new(fst_stream: raw::Stream<'s, A>) -> Self { Stream(fst_stream) } /// Convert this stream into a vector of Unicode strings. /// /// If any key is not valid UTF-8, then iteration on the stream is stopped /// and a UTF-8 decoding error is returned. /// /// Note that this creates a new allocation for every key in the stream. pub fn into_strs(self) -> Result<Vec<String>> { self.0.into_str_keys() } /// Convert this stream into a vector of byte strings. /// /// Note that this creates a new allocation for every key in the stream. pub fn into_bytes(self) -> Vec<Vec<u8>> { self.0.into_byte_keys() } } impl<'a, 's, A: Automaton> Streamer<'a> for Stream<'s, A> { type Item = &'a [u8]; fn next(&'a mut self) -> Option<Self::Item> { self.0.next().map(|(key, _)| key) } } /// A builder for constructing range queries on streams. /// /// Once all bounds are set, one should call `into_stream` to get a /// `Stream`. /// /// Bounds are not additive. That is, if `ge` is called twice on the same /// builder, then the second setting wins. /// /// The `A` type parameter corresponds to an optional automaton to filter /// the stream. By default, no filtering is done. /// /// The `'s` lifetime parameter refers to the lifetime of the underlying set. pub struct StreamBuilder<'s, A=AlwaysMatch>(raw::StreamBuilder<'s, A>); impl<'s, A: Automaton> StreamBuilder<'s, A> { /// Specify a greater-than-or-equal-to bound. pub fn ge<T: AsRef<[u8]>>(self, bound: T) -> Self { StreamBuilder(self.0.ge(bound)) } /// Specify a greater-than bound. pub fn gt<T: AsRef<[u8]>>(self, bound: T) -> Self { StreamBuilder(self.0.gt(bound)) } /// Specify a less-than-or-equal-to bound. pub fn le<T: AsRef<[u8]>>(self, bound: T) -> Self { StreamBuilder(self.0.le(bound)) } /// Specify a less-than bound. pub fn lt<T: AsRef<[u8]>>(self, bound: T) -> Self { StreamBuilder(self.0.lt(bound)) } } impl<'s, 'a, A: Automaton> IntoStreamer<'a> for StreamBuilder<'s, A> { type Item = &'a [u8]; type Into = Stream<'s, A>; fn into_stream(self) -> Self::Into { Stream(self.0.into_stream()) } } /// A builder for collecting set streams on which to perform set operations. /// /// Set operations include intersection, union, difference and symmetric /// difference. The result of each set operation is itself a stream that emits /// keys in lexicographic order. /// /// All set operations work efficiently on an arbitrary number of /// streams with memory proportional to the number of streams. /// /// The algorithmic complexity of all set operations is `O(n1 + n2 + n3 + ...)` /// where `n1, n2, n3, ...` correspond to the number of elements in each /// stream. /// /// The `'s` lifetime parameter refers to the lifetime of the underlying set. pub struct OpBuilder<'s>(raw::OpBuilder<'s>); impl<'s> OpBuilder<'s> { /// Create a new set operation builder. pub fn new() -> Self { OpBuilder(raw::OpBuilder::new()) } /// Add a stream to this set operation. /// /// This is useful for a chaining style pattern, e.g., /// `builder.add(stream1).add(stream2).union()`. /// /// The stream must emit a lexicographically ordered sequence of byte /// strings. pub fn add<I, S>(mut self, streamable: I) -> Self where I: for<'a> IntoStreamer<'a, Into=S, Item=&'a [u8]>, S: 's + for<'a> Streamer<'a, Item=&'a [u8]> { self.push(streamable); self } /// Add a stream to this set operation. /// /// The stream must emit a lexicographically ordered sequence of byte /// strings. pub fn push<I, S>(&mut self, streamable: I) where I: for<'a> IntoStreamer<'a, Into=S, Item=&'a [u8]>, S: 's + for<'a> Streamer<'a, Item=&'a [u8]> { self.0.push(StreamZeroOutput(streamable.into_stream())); } /// Performs a union operation on all streams that have been added. /// /// # Example /// /// ```rust /// use fst::{IntoStreamer, Streamer, Set}; /// /// let set1 = Set::from_iter(&["a", "b", "c"]).unwrap(); /// let set2 = Set::from_iter(&["a", "y", "z"]).unwrap(); /// /// let mut union = set1.op().add(&set2).union(); /// /// let mut keys = vec![]; /// while let Some(key) = union.next() { /// keys.push(key.to_vec()); /// } /// assert_eq!(keys, vec![b"a", b"b", b"c", b"y", b"z"]); /// ``` pub fn union(self) -> Union<'s> { Union(self.0.union()) } /// Performs an intersection operation on all streams that have been added. /// /// # Example /// /// ```rust /// use fst::{IntoStreamer, Streamer, Set}; /// /// let set1 = Set::from_iter(&["a", "b", "c"]).unwrap(); /// let set2 = Set::from_iter(&["a", "y", "z"]).unwrap(); /// /// let mut intersection = set1.op().add(&set2).intersection(); /// /// let mut keys = vec![]; /// while let Some(key) = intersection.next() { /// keys.push(key.to_vec()); /// } /// assert_eq!(keys, vec![b"a"]); /// ``` pub fn intersection(self) -> Intersection<'s> { Intersection(self.0.intersection()) } /// Performs a difference operation with respect to the first stream added. /// That is, this returns a stream of all elements in the first stream /// that don't exist in any other stream that has been added. /// /// # Example /// /// ```rust /// use fst::{IntoStreamer, Streamer, Set}; /// /// let set1 = Set::from_iter(&["a", "b", "c"]).unwrap(); /// let set2 = Set::from_iter(&["a", "y", "z"]).unwrap(); /// /// let mut difference = set1.op().add(&set2).difference(); /// /// let mut keys = vec![]; /// while let Some(key) = difference.next() { /// keys.push(key.to_vec()); /// } /// assert_eq!(keys, vec![b"b", b"c"]); /// ``` pub fn difference(self) -> Difference<'s> { Difference(self.0.difference()) } /// Performs a symmetric difference operation on all of the streams that /// have been added. /// /// When there are only two streams, then the keys returned correspond to /// keys that are in either stream but *not* in both streams. /// /// More generally, for any number of streams, keys that occur in an odd /// number of streams are returned. /// /// # Example /// /// ```rust /// use fst::{IntoStreamer, Streamer, Set}; /// /// let set1 = Set::from_iter(&["a", "b", "c"]).unwrap(); /// let set2 = Set::from_iter(&["a", "y", "z"]).unwrap(); /// /// let mut sym_difference = set1.op().add(&set2).symmetric_difference(); /// /// let mut keys = vec![]; /// while let Some(key) = sym_difference.next() { /// keys.push(key.to_vec()); /// } /// assert_eq!(keys, vec![b"b", b"c", b"y", b"z"]); /// ``` pub fn symmetric_difference(self) -> SymmetricDifference<'s> { SymmetricDifference(self.0.symmetric_difference()) } } impl<'f, I, S> Extend<I> for OpBuilder<'f> where I: for<'a> IntoStreamer<'a, Into=S, Item=&'a [u8]>, S: 'f + for<'a> Streamer<'a, Item=&'a [u8]> { fn extend<T>(&mut self, it: T) where T: IntoIterator<Item=I> { for stream in it { self.push(stream); } } } impl<'f, I, S> FromIterator<I> for OpBuilder<'f> where I: for<'a> IntoStreamer<'a, Into=S, Item=&'a [u8]>, S: 'f + for<'a> Streamer<'a, Item=&'a [u8]> { fn from_iter<T>(it: T) -> Self where T: IntoIterator<Item=I> { let mut op = OpBuilder::new(); op.extend(it); op } } /// A stream of set union over multiple streams in lexicographic order. /// /// The `'s` lifetime parameter refers to the lifetime of the underlying set. pub struct Union<'s>(raw::Union<'s>); impl<'a, 's> Streamer<'a> for Union<'s> { type Item = &'a [u8]; fn next(&'a mut self) -> Option<Self::Item> { self.0.next().map(|(key, _)| key) } } /// A stream of set intersection over multiple streams in lexicographic order. /// /// The `'s` lifetime parameter refers to the lifetime of the underlying set. pub struct Intersection<'s>(raw::Intersection<'s>); impl<'a, 's> Streamer<'a> for Intersection<'s> { type Item = &'a [u8]; fn next(&'a mut self) -> Option<Self::Item> { self.0.next().map(|(key, _)| key) } } /// A stream of set difference over multiple streams in lexicographic order. /// /// The difference operation is taken with respect to the first stream and the /// rest of the streams. i.e., All elements in the first stream that do not /// appear in any other streams. /// /// The `'s` lifetime parameter refers to the lifetime of the underlying set. pub struct Difference<'s>(raw::Difference<'s>); impl<'a, 's> Streamer<'a> for Difference<'s> { type Item = &'a [u8]; fn next(&'a mut self) -> Option<Self::Item> { self.0.next().map(|(key, _)| key) } } /// A stream of set symmetric difference over multiple streams in lexicographic /// order. /// /// The `'s` lifetime parameter refers to the lifetime of the underlying set. pub struct SymmetricDifference<'s>(raw::SymmetricDifference<'s>); impl<'a, 's> Streamer<'a> for SymmetricDifference<'s> { type Item = &'a [u8]; fn next(&'a mut self) -> Option<Self::Item> { self.0.next().map(|(key, _)| key) } } /// A specialized stream for mapping set streams (`&[u8]`) to streams used /// by raw fsts (`(&[u8], Output)`). /// /// If this were iterators, we could use `iter::Map`, but doing this on streams /// requires HKT, so we need to write out the monomorphization ourselves. struct StreamZeroOutput<S>(S); impl<'a, S: Streamer<'a>> Streamer<'a> for StreamZeroOutput<S> { type Item = (S::Item, raw::Output); fn next(&'a mut self) -> Option<Self::Item> { self.0.next().map(|key| (key, raw::Output::zero())) } }