Join

In Rust, consider a string vector that contains strings. We can join these string elements together into a single descriptive string.

With a delimiter string, we can place characters in between the elements in the resulting string. Any string can be used as a delimiter.

First example

Here we have a string array of just 2 elements. The type of the array is implicit here, but it could be specified with more syntax.

fn main() {
    // Create an array of strings.
    let patterns = ["abc", "def"];

    // Join together the results into a string.
    let result = patterns.join(",");
    println!("JOIN: {}", result);
}
JOIN: abc,def

String vector

In Rust, join() acts upon a slice. And a string array, string slice, or string vector can be used as a slice—no special conversions are needed.

fn main() {
    let mut landmarks = vec!["mountain", "hill"];
    landmarks.push("valley");
    landmarks.push("river");

    // Join the string vector on another string.
    // ... Two characters can be used.
    let result = landmarks.join("++");
    println!("JOIN: {}", result);
}
JOIN: mountain++hill++valley++river

Split and join

Conceptually, split() and join() are opposites—they separate and merge string elements. We demonstrate this by using split, then join(), to get the original string.

fn main() {
    let input = "a b c";

    // Split on space into a vector.
    let v: Vec<_> = input.split(' ').collect();

    // Join with space to get the original string back again.
    let j = v.join(" ");

    // Test result.
    if input == j {
        println!("SPLIT-JOIN ROUNDTRIP OK: {}/{}", input, j);
    }
}
SPLIT-JOIN ROUNDTRIP OK: a b c/a b c

Join is useful in many Rust programs, and an obsolete connect() method has the same effect as join. Join and split can be used together for full round-trip parsing.