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Add a "peekable" iterator adaptor, with a peek() method that returns the next element. #8428

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Add a "peekable" iterator adaptor, with a peek() method that returns the next element. #8428

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b44f423
std::iterator: Rename .peek() to .inspect()
Aug 10, 2013
deb7b67
Add a "peekable" iterator adaptor, with a peek() method that returns …
SimonSapin Aug 8, 2013
0b35e3b
extra::treemap: Use IteratorUtil::peekable
Aug 9, 2013
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134 changes: 46 additions & 88 deletions src/libextra/treemap.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,8 @@


use std::util::{swap, replace};
use std::iterator::{FromIterator, Extendable};
use std::iterator::{FromIterator, Extendable, Peekable};
use std::cmp::Ordering;

// This is implemented as an AA tree, which is a simplified variation of
// a red-black tree where red (horizontal) nodes can only be added
Expand Down Expand Up @@ -529,24 +530,24 @@ impl<T: TotalOrd> TreeSet<T> {

/// Visit the values (in-order) representing the difference
pub fn difference<'a>(&'a self, other: &'a TreeSet<T>) -> Difference<'a, T> {
Difference{a: Focus::new(self.iter()), b: Focus::new(other.iter())}
Difference{a: self.iter().peekable(), b: other.iter().peekable()}
}

/// Visit the values (in-order) representing the symmetric difference
pub fn symmetric_difference<'a>(&'a self, other: &'a TreeSet<T>)
-> SymDifference<'a, T> {
SymDifference{a: Focus::new(self.iter()), b: Focus::new(other.iter())}
SymDifference{a: self.iter().peekable(), b: other.iter().peekable()}
}

/// Visit the values (in-order) representing the intersection
pub fn intersection<'a>(&'a self, other: &'a TreeSet<T>)
-> Intersection<'a, T> {
Intersection{a: Focus::new(self.iter()), b: Focus::new(other.iter())}
Intersection{a: self.iter().peekable(), b: other.iter().peekable()}
}

/// Visit the values (in-order) representing the union
pub fn union<'a>(&'a self, other: &'a TreeSet<T>) -> Union<'a, T> {
Union{a: Focus::new(self.iter()), b: Focus::new(other.iter())}
Union{a: self.iter().peekable(), b: other.iter().peekable()}
}
}

Expand All @@ -560,61 +561,47 @@ pub struct TreeSetRevIterator<'self, T> {
priv iter: TreeMapRevIterator<'self, T, ()>
}

// Encapsulate an iterator and hold its latest value until stepped forward
struct Focus<A, T> {
priv iter: T,
priv focus: Option<A>,
}

impl<A, T: Iterator<A>> Focus<A, T> {
fn new(mut it: T) -> Focus<A, T> {
Focus{focus: it.next(), iter: it}
}
fn step(&mut self) {
self.focus = self.iter.next()
}
}

/// Lazy iterator producing elements in the set difference (in-order)
pub struct Difference<'self, T> {
priv a: Focus<&'self T, TreeSetIterator<'self, T>>,
priv b: Focus<&'self T, TreeSetIterator<'self, T>>,
priv a: Peekable<&'self T, TreeSetIterator<'self, T>>,
priv b: Peekable<&'self T, TreeSetIterator<'self, T>>,
}

/// Lazy iterator producing elements in the set symmetric difference (in-order)
pub struct SymDifference<'self, T> {
priv a: Focus<&'self T, TreeSetIterator<'self, T>>,
priv b: Focus<&'self T, TreeSetIterator<'self, T>>,
priv a: Peekable<&'self T, TreeSetIterator<'self, T>>,
priv b: Peekable<&'self T, TreeSetIterator<'self, T>>,
}

/// Lazy iterator producing elements in the set intersection (in-order)
pub struct Intersection<'self, T> {
priv a: Focus<&'self T, TreeSetIterator<'self, T>>,
priv b: Focus<&'self T, TreeSetIterator<'self, T>>,
priv a: Peekable<&'self T, TreeSetIterator<'self, T>>,
priv b: Peekable<&'self T, TreeSetIterator<'self, T>>,
}

/// Lazy iterator producing elements in the set intersection (in-order)
pub struct Union<'self, T> {
priv a: Focus<&'self T, TreeSetIterator<'self, T>>,
priv b: Focus<&'self T, TreeSetIterator<'self, T>>,
priv a: Peekable<&'self T, TreeSetIterator<'self, T>>,
priv b: Peekable<&'self T, TreeSetIterator<'self, T>>,
}

/// Compare `x` and `y`, but return `short` if x is None and `long` if y is None
fn cmp_opt<T: TotalOrd>(x: Option<&T>, y: Option<&T>,
short: Ordering, long: Ordering) -> Ordering {
match (x, y) {
(None , _ ) => short,
(_ , None ) => long,
(Some(x1), Some(y1)) => x1.cmp(y1),
}
}

impl<'self, T: TotalOrd> Iterator<&'self T> for Difference<'self, T> {
fn next(&mut self) -> Option<&'self T> {
loop {
match (self.a.focus, self.b.focus) {
(None , _ ) => return None,
(ret , None ) => { self.a.step(); return ret },
(Some(a1), Some(b1)) => {
let cmp = a1.cmp(b1);
if cmp == Less {
self.a.step();
return Some(a1);
} else {
if cmp == Equal { self.a.step() }
self.b.step();
}
}
match cmp_opt(self.a.peek(), self.b.peek(), Less, Less) {
Less => return self.a.next(),
Equal => { self.a.next(); self.b.next(); }
Greater => { self.b.next(); }
}
}
}
Expand All @@ -623,23 +610,10 @@ impl<'self, T: TotalOrd> Iterator<&'self T> for Difference<'self, T> {
impl<'self, T: TotalOrd> Iterator<&'self T> for SymDifference<'self, T> {
fn next(&mut self) -> Option<&'self T> {
loop {
match (self.a.focus, self.b.focus) {
(ret , None ) => { self.a.step(); return ret },
(None , ret ) => { self.b.step(); return ret },
(Some(a1), Some(b1)) => {
let cmp = a1.cmp(b1);
if cmp == Less {
self.a.step();
return Some(a1);
} else {
self.b.step();
if cmp == Greater {
return Some(b1);
} else {
self.a.step();
}
}
}
match cmp_opt(self.a.peek(), self.b.peek(), Greater, Less) {
Less => return self.a.next(),
Equal => { self.a.next(); self.b.next(); }
Greater => return self.b.next(),
}
}
}
Expand All @@ -648,20 +622,16 @@ impl<'self, T: TotalOrd> Iterator<&'self T> for SymDifference<'self, T> {
impl<'self, T: TotalOrd> Iterator<&'self T> for Intersection<'self, T> {
fn next(&mut self) -> Option<&'self T> {
loop {
match (self.a.focus, self.b.focus) {
(None , _ ) => return None,
(_ , None ) => return None,
(Some(a1), Some(b1)) => {
let cmp = a1.cmp(b1);
if cmp == Less {
self.a.step();
} else {
self.b.step();
if cmp == Equal {
return Some(a1);
}
}
},
let o_cmp = match (self.a.peek(), self.b.peek()) {
(None , _ ) => None,
(_ , None ) => None,
(Some(a1), Some(b1)) => Some(a1.cmp(b1)),
};
match o_cmp {
None => return None,
Some(Less) => { self.a.next(); }
Some(Equal) => { self.b.next(); return self.a.next() }
Some(Greater) => { self.b.next(); }
}
}
}
Expand All @@ -670,22 +640,10 @@ impl<'self, T: TotalOrd> Iterator<&'self T> for Intersection<'self, T> {
impl<'self, T: TotalOrd> Iterator<&'self T> for Union<'self, T> {
fn next(&mut self) -> Option<&'self T> {
loop {
match (self.a.focus, self.b.focus) {
(ret , None) => { self.a.step(); return ret },
(None , ret ) => { self.b.step(); return ret },
(Some(a1), Some(b1)) => {
let cmp = a1.cmp(b1);
if cmp == Greater {
self.b.step();
return Some(b1);
} else {
self.a.step();
if cmp == Equal {
self.b.step();
}
return Some(a1);
}
}
match cmp_opt(self.a.peek(), self.b.peek(), Greater, Less) {
Less => return self.a.next(),
Equal => { self.b.next(); return self.a.next() }
Greater => return self.b.next(),
}
}
}
Expand Down
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