Starts with

In Rust we can test the beginnings and ends of strings with starts_with and ends_with. Sometimes we may need to borrow from a String to get a str reference.

For some tests, we can take a slice of a string and compare it against a string literal. But starts_with and ends_with are usually easier to read.

Example

To begin, we create 2 strings with the String new() function and push_str. These are String objects, not str references. We call functions on the Strings.

fn main() {
    let mut data = String::new();
    data.push_str("abcdef");

    // Test with str reference argument directly.
    if data.starts_with("abc") {
        println!("STARTS WITH ABC");
    }

    let mut end = String::new();
    end.push_str("def");

    // Borrow the String to get a str reference.
    if data.ends_with(&end) {
        println!("ENDS WITH DEF");
    }
}
STARTS WITH ABC
ENDS WITH DEF

First char

We can take a slice of a string with a range index. And when we borrow the slice, we can compare it against a string literal.

fn main() {
    let mut data = String::new();
    data.push_str("Cat");

    // Test first letter of String.
    if &data[0..1] == "C" {
        println!("STARTS WITH C")
    }
}
STARTS WITH C

We reviewed some ways to test beginnings and ends of strings in Rust. We can use starts_with, ends_with, and even test string ranges with borrowing directly.