String

The String data type is a linear series of characters encoded as UTF-8. It is useful for storing textual data.

Creating a String

A String can be created using the String::new() or String::from() associated functions. Many types have a to_string method to produce a string e.g. from a number.

let my_string = String::from("The answer is");
let answer = 42.to_string();
println!("{my_string} {answer}");

The format! Macro

Because producing a large string from a selection of smaller data types is a common operation, Rust also has a shorthand which elides the details of calling to_string: the format! macro. For example, we could simplify the construction of the composite string above as follows:

let the_answer = format!("{} {}.", "The answer is", 42);
assert_eq!("The answer is 42.", the_answer);

String Slices

Strings have a close relationship with string slices. String slices are immutable references to a region of memory of known size, containing a linear series of characters encoded as UTF-8. Any string can be coerced into a string slice by borrowing with the dereference (&) operator. To convert a string slice to a string, the to_string() method or String::from are both appropriate.

In Rust code, a literal string is enclosed in double-quotes. These string literals are always string slices, because they refer to an immutable region of memory within the program’s executable.

let string = String::from("string");
let slice = "string";
assert_eq!(slice, &string);

Mutating a String

To concatenate a single character to a string, use the push method. To concatenate a string slice to a string, use the push_str method or the + operator.

fn main() {
    // For demonstration purposes, we're not using `format!`
    let s1 = String::from("tic");
    let s2 = String::from("tac");
    let s3 = String::from("toe");

    let s = s1 + "-" + &s2 + "-" + &s3;
    println!("{s}");
}

Accessing Characters in a String

Since Rust strings are UTF-8 encoded individual characters are not all of the same size. Thus the String data type does not provide an indexing operator ([]). To access all the characters or a specific character in a string, the chars() method can be used. This iterates over each character in the string, in sequence.

let alphabet: String = ('a'..='z').collect();
for c in alphabet.chars() {
    println!("{c}");
}
let j = alphabet.chars().nth(9);
println!("{j:?}"); // prints Some('j')

More

String is a rich datatype with several methods and macros built around it. Check out the standard library documentation for all of the member methods and functionality provided by String.

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Originally from Exercism rust concepts