`Join`

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

Delimiter info

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.

Info With join, we place a comma character in between the 2 elements in the array. The result is a single string.

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.

Here We join the strings in a vector of terrain landmarks. We use a 2-character delimiter for the output string, and print it.

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.

Detail With split() we place the letters into a Vec, and then we call join with the same delimiter to go back to the original data.

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

Summary

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.

Join