Strings and collections · Coding Class

Basics · Build a program← Read the Learn chapter

Apply the chapter in three steps: an exercise, a program project, and a debugging task. Implement first, then consult the hints and completion criteria. Use a separate file or working directory for each task.

1. Exercise · Distinguish bytes and empty items

Print "한".len() and the length after splitting " red green\tblue " on ASCII whitespace.

Completion: Both results are 3: bytes in the first case, words in the second.

Hint: std.string.split_ascii_whitespace does not produce empty words.

2. Build a program · Build a score summary

Write a function accepting Vec<Int> that prints the count and total for [10, 20, 30]. Also call it with an empty vector. Iterate over indices without iterators.

Completion: The first call reports count 3 and total 60; empty input reports 0 and 0.

Hint: A 0..values.len() loop also handles empty input.

3. Debug · Fix empty-vector access

The code below checks successfully but fails at runtime. Print empty for an empty vector, otherwise print the first element.

Start with this deliberately broken program.

class_empty.xen

fn main() {
    let values: Vec<Int> = [];
    println(values.get(0));
}

xen run class_empty.xen

Diagnostic excerpt:

class_empty.stderr

vector index out of bounds

Completion: [] prints empty, [7] prints 7, and both exit successfully.

Hint: get() does not return Option. Check length before calling it.

Verify and record

Use xen check file.xen followed by xen run file.xen for ordinary programs; use xen test file.xen for test-only files. Record the original error, its cause, and the corrected result, then rerun every input in the completion criteria.