for loops

for and range

The for in construct can be used to iterate through an Iterator. One of the easiest ways to create an iterator is to use the range notation a..b. This yields values from a (inclusive) to b (exclusive) in steps of one.

Let's write FizzBuzz using for instead of while.

fn main() {
    // `n` will take the values: 1, 2, ..., 100 in each iteration
    for n in 1..101_u8 {
        if n % 15 == 0 {
            println!("fizzbuzz");
        } else if n % 3 == 0 {
            println!("fizz");
        } else if n % 5 == 0 {
            println!("buzz");
        } else {
            println!("{}", n);
        }
    }
}

Alternatively, a..=b can be used for a range that is inclusive on both ends. The above can be written as:

fn main() {
    // `n` will take the values: 1, 2, ..., 100 in each iteration
    for n in 1..= 100_u8 {
        if n % 15 == 0 {
            println!("fizzbuzz");
        } else if n % 3 == 0 {
            println!("fizz");
        } else if n % 5 == 0 {
            println!("buzz");
        } else {
            println!("{}", n);
        }
    }
}

for and iterators

The for in construct is able to interact with an Iterator in several ways. As discussed in the section on the Iterator trait, by default the for loop will apply the into_iter function to the collection. However, this is not the only means of converting collections into iterators.

into_iter consumes the collection so that on each iteration the exact data is provided. Once the collection has been consumed it is no longer available for reuse as it has been 'moved' within the loop.

• into_iter - This consumes the collection so that on each iteration the exact data is provided. Once the collection has been consumed it is no longer available for reuse as it has been 'moved' within the loop.

fn main() {
    let names: Array<ByteArray> = array!["Bob", "Frank", "Ferris"];

    for name in names.into_iter() {
        if name == "Ferris" {
            println!("There is a caironaute among us!");
        } else {
            println!("Hello {}", name);
        }
    }

    println!("names: {:?}", names);
    // FIXME ^ Comment out this line
}

Note: The syntax for elem in collection is equivalent to for elem in collection.into_iter() and requires the IntoIter trait to be implemented for the collection.

In the above snippets note the type of match branch, that is the key difference in the types of iteration. The difference in type then of course implies differing actions that are able to be performed.

See also:

Iterator