Strings and collections

Use Vec<T> to keep several values in order. Find text splitting functions in std.string. Save this as collections.xen:

use std.string as text;

fn main() {
    let words = text.split_ascii_whitespace("red green blue");
    println(words.get(1));
    println("한".len());
    let mut scores: Vec<Int> = [];
    scores.push(10);
    scores.push(20);
    scores[0] = 11;
    println(scores);
    let view = scores.slice(0, 2);
    println(view.get(1));
}

$ xen run collections.xen
green
3
[11, 20]
20

Strings

A String is an immutable sequence of bytes. Joining strings with + creates a new string. len() counts bytes, not characters: "한" occupies three bytes in UTF-8. Character indexing and string mutation syntax are unavailable.

Inside a string, use \n, \t, \r, \", and \\. Xen does not automatically validate UTF-8, so file contents retain their original bytes. Cutting at byte positions can split a character’s encoding.

std.string.split_ascii_whitespace splits at ASCII whitespace, including spaces, tabs, and newlines, without producing empty items. split_byte(text, u8(44)) splits at comma bytes and keeps empty items. It does not interpret CSV quoting. See the standard library for searching and extracting parts.

Vectors

Create a vector with [10, 20]. Give an empty vector an element type such as Vec<Int>. Indices start at zero.

Task	Expression
Count items	scores.len()
Read	scores[0] or scores.get(0)
Add or change	scores.push(30), scores.set(0, 12)
Remove the last item	scores.pop()
Replace and return the previous item	scores.replace(0, 12)
Exchange two items	scores.swap(0, 1)

Changes require let mut. An invalid index or pop() on an empty vector causes a runtime error. Check the length first. get() does not return an Option on failure. All elements must have the same type. References, slices, and pointers cannot be vector elements.

Move-only elements such as Box and File cannot be copied through indexing or get(). Take ownership with pop(), replace(), or .into_iter(), or create a shared element reference with &values[index] in a function with explc. While that reference remains in use, you cannot change or move the entire vector. Mutable element references are unavailable.

String.as_bytes() creates a read-only Slice<U8>. Vec<U8>.into_string() consumes the vector and transfers its bytes into a string without UTF-8 validation.

Read-only views

as_slice() creates a Slice<T> over the whole vector; slice(start, end) views a range with an excluded end. This does not copy the elements into a new vector. You cannot change or move the original until the view’s last use. Views cannot be returned from a function or stored in vectors; mutable views are unavailable. Copy items into a new vector if you need independent storage.

Iteration and transformations

Loop over indices using a range, or add use std.iter; and call .iter(). for value in values does not automatically turn a vector into an iterator.

use std.iter;

fn doubled(value: Int) -> Int {
    return value * 2;
}

#![explc]
fn over_two(value: &Int) -> Bool {
    return *value > 2;
}

fn main() {
    let values = [1, 2, 3];
    for value in values.iter().map(doubled).filter(over_two) {
        println(value);
    }
}

$ xen run iterators.xen
4
6

.map transforms each item and .filter keeps matching items. The functions run when you iterate. Supply named functions as callbacks. .enumerate() yields tuples containing a zero-based index and a value.

Vector and Slice .iter() calls require copyable or cloneable elements. You cannot change the source while a borrowed .iter() chain remains in use. .into_iter() takes ownership of the vector and yields its items in order. For move-only items such as Box or File, use .into_iter() or read through an element reference as described above. After .into_iter(), the original vector is no longer available. See copies and moves.