Range

It is possible to create custom structs in Rust that store start and end indexes, but the Range struct can do this in a more standard way. We can use Range from std ops.

A generic type, Range can represent its start and end with a numeric type like usize. It is possible to use special, shortened syntax to create a Range.

Example

This program uses the Range struct within a struct, and as a local variable in the main function. We can get a slice from an array with a Range.

Part 1 The Example struct has a field of type Range(usize) and this means the Range has a start and end with usize values.

Part 2 We create an instance of the Example struct, specifying the start and end based on same-named local variables.

Part 3 We can use a shortened syntax to create a Range: we use 2 periods in between the start and end values.

Part 4 A range (even a local Range variable) can be used index an array or other slice and get a slice.

Part 5 For convenience, the Range struct provides a contains() function, and this can be used to see if a value falls within a range.

use std::ops::Range;

// Part 1: use Range as a field in a struct.
struct Example {
    range: Range<usize>,
}

fn main() {
    // Part 2: create struct containing range with 2 integers.
    let start = 10;
    let end = 20;
    let example = Example {
        range: Range { start, end },
    };
    println!("{:?}", example.range);

    // Part 3: create struct containing range with simpler syntax.
    let example2 = Example { range: start..end };
    println!("{:?}", example2.range);

    // Part 4: use inclusive range, and print values from array directly with named range.
    let bytes = [100, 101, 102, 103, 104];
    let range = 2..=4;
    println!(
        "{:?} {:?} {:?}",
        range.clone(),
        &bytes[range],
        &bytes[2..=4]
    );

    // Part 5: see if range contains an integer.
    let range2 = 5..15;
    if range2.contains(&10) {
        println!("Range contains 10!");
    }
}10..20
10..20
2..=4 [102, 103, 104] [102, 103, 104]
Range contains 10!

Summary

Ranges are used frequently in Rust programs, and every time we use the short range syntax to get a slice, we are creating a range. Range is found in the standard library (std ops).