Struct std::iter::Peekable
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[src]
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
pub struct Peekable<I> where I: Iterator {
// some fields omitted
}An iterator with a peek() that returns an optional reference to the next
element.
This struct is created by the peekable() method on Iterator. See its
documentation for more.
Methods
impl<I> Peekable<I> where I: Iterator
fn peek(&mut self) -> Option<&I::Item>
Returns a reference to the next() value without advancing the iterator.
The peek() method will return the value that a call to next() would
return, but does not advance the iterator. Like next(), if there is
a value, it's wrapped in a Some(T), but if the iterator is over, it
will return None.
Because peek() returns reference, and many iterators iterate over
references, this leads to a possibly confusing situation where the
return value is a double reference. You can see this effect in the
examples below, with &&i32.
Examples
Basic usage:
let xs = [1, 2, 3]; let mut iter = xs.iter().peekable(); // peek() lets us see into the future assert_eq!(iter.peek(), Some(&&1)); assert_eq!(iter.next(), Some(&1)); assert_eq!(iter.next(), Some(&2)); // we can peek() multiple times, the itererator won't advance assert_eq!(iter.peek(), Some(&&3)); assert_eq!(iter.peek(), Some(&&3)); assert_eq!(iter.next(), Some(&3)); // after the itererator is finished, so is peek() assert_eq!(iter.peek(), None); assert_eq!(iter.next(), None);
fn is_empty(&mut self) -> bool
Unstable (
core): the libcore library has not yet been scrutinized for stabilization in terms of structure and naming
Checks if the iterator has finished iterating.
Returns true if there are no more elements in the iterator, and
false if there are.
Examples
Basic usage:
#![feature(core)] let xs = [1, 2, 3]; let mut iter = xs.iter().peekable(); // there are still elements to iterate over assert_eq!(iter.is_empty(), false); // let's consume the iterator iter.next(); iter.next(); iter.next(); assert_eq!(iter.is_empty(), true);