pub fn once<T>(value: T) -> Once<T> ⓘExpand description
Creates an iterator that yields an element exactly once.
This is commonly used to adapt a single value into a chain() of other
kinds of iteration. Maybe you have an iterator that covers almost
everything, but you need an extra special case. Maybe you have a function
which works on iterators, but you only need to process one value.
§Examples
Basic usage:
use std::iter;
// one is the loneliest number
let mut class="number">1);
assert_eq!(Some(1), one.next());
// just one, that's all we get
assert_eq!(None, one.next());Chaining together with another iterator. Let’s say that we want to iterate
over each file of the .foo directory, but also a configuration file,
.foorc:
use std::iter;
use std::fs;
use std::path::PathBuf;
let dirs = fs::read_dir(".foo")?;
// we need to convert from an iterator of DirEntry-s to an iterator of
// PathBufs, so we use map
let dirs = dirs.map(|file| file.unwrap().path());
// now, our iterator just for our config file
let config = iter::once(PathBuf::from(".foorc"));
// chain the two iterators together into one big iterator
let files = dirs.chain(config);
// this will give us all of the files in .foo as well as .foorc
for f in files {
println!("{f:?}");
}