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Implement Hash and PartialOrd for RingBuf #16020

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merged 3 commits into from
Jul 27, 2014
Merged

Implement Hash and PartialOrd for RingBuf #16020

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1cfa656
Implement Hash for RingBuf
nham Jul 27, 2014
6361577
Implement PartialOrd for RingBuf
nham Jul 27, 2014
9fa4424
Hash the length of the RingBuf before hashing elements
nham Jul 27, 2014
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49 changes: 49 additions & 0 deletions src/libcollections/ringbuf.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,8 @@ use core::cmp;
use core::default::Default;
use core::fmt;
use core::iter::RandomAccessIterator;
use core::iter;
use std::hash::{Writer, Hash};

use {Deque, Collection, Mutable, MutableSeq};
use vec::Vec;
Expand Down Expand Up @@ -450,6 +452,21 @@ impl<A: PartialEq> PartialEq for RingBuf<A> {
}
}

impl<A: PartialOrd> PartialOrd for RingBuf<A> {
fn partial_cmp(&self, other: &RingBuf<A>) -> Option<Ordering> {
iter::order::partial_cmp(self.iter(), other.iter())
}
}

impl<S: Writer, A: Hash<S>> Hash<S> for RingBuf<A> {
fn hash(&self, state: &mut S) {
self.len().hash(state);
for elt in self.iter() {
elt.hash(state);
}
}
}
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I think in general collections need to hash their length first because otherwise this would have the same hash:

  • (vec![1], vec![2, 3])
  • (vec![1, 2], vec![3])

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Interesting, I didn't' think of that. That means that some of the other Hash implementations I've done are wrong. TreeMap at least seems to be wrong. Though I'm wondering if that could be fixed at the tuple-level. (Tuples could hash the index before each value?)

I've fixed it for RingBuf here.

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Ah I think it's ok, they can be amended in the future. Hashing to the same value isn't really the end of the world, so long as the comparisons are correct!


impl<A> FromIterator<A> for RingBuf<A> {
fn from_iter<T: Iterator<A>>(iterator: T) -> RingBuf<A> {
let (lower, _) = iterator.size_hint();
Expand Down Expand Up @@ -485,6 +502,7 @@ mod tests {
use std::fmt::Show;
use std::prelude::*;
use std::gc::{GC, Gc};
use std::hash;
use test::Bencher;
use test;

Expand Down Expand Up @@ -912,6 +930,37 @@ mod tests {
assert!(e == RingBuf::new());
}

#[test]
fn test_hash() {
let mut x = RingBuf::new();
let mut y = RingBuf::new();

x.push(1i);
x.push(2);
x.push(3);

y.push(0i);
y.push(1i);
y.pop_front();
y.push(2);
y.push(3);

assert!(hash::hash(&x) == hash::hash(&y));
}

#[test]
fn test_ord() {
let x = RingBuf::new();
let mut y = RingBuf::new();
y.push(1i);
y.push(2);
y.push(3);
assert!(x < y);
assert!(y > x);
assert!(x <= x);
assert!(x >= x);
}

#[test]
fn test_show() {
let ringbuf: RingBuf<int> = range(0i, 10).collect();
Expand Down