Example
There are 4 looping constructs in Rust. All examples below produce the same output.
Infinite Loops
let mut x = 0;
loop {
if x > 3 { break; }
println!("{}", x);
x += 1;
}
While Loops
let mut x = 0;
while x <= 3 {
println!("{}", x);
x += 1;
}
Also see: What is the difference between loop and while true?
Pattern-matched While Loops
These are sometimes known as while let loops for brevity.
let mut x = Some(0);
while let Some(v) = x {
println!("{}", v);
x = if v < 3 { Some(v + 1) }
else { None };
}
This is equivalent to a match inside a loop block:
let mut x = Some(0);
loop {
match x {
Some(v) => {
println!("{}", v);
x = if v < 3 { Some(v + 1) }
else { None };
}
_ => break,
}
}
For Loops
In Rust, for loop can only be used with an "iterable" object (i.e. it should implement IntoIterator).
for x in 0..4 {
println!("{}", x);
}
This is equivalent to the following snippet involving while let:
let mut iter = (0..4).into_iter();
while let Some(v) = iter.next() {
println!("{}", v);
}
Note: 0..4 returns a Range object which already implements the Iterator trait. Therefore into_iter() is unnecessary, but is kept just to illustrate what for does. For an in-depth look, see the official docs on for Loops and IntoIterator.
Also see: Iterators
